diff --git a/PRESUBMIT.py b/PRESUBMIT.py
index b7a443f458c..d4a4ac2de16 100644
--- a/PRESUBMIT.py
+++ b/PRESUBMIT.py
@@ -247,7 +247,7 @@ def _CheckClangTidy(input_api, output_api):
     files = []
     for f in input_api.AffectedFiles():
         path = f.LocalPath()
-        if is_cpp_file(path): files.append(path)
+        if is_cpp_file(path) and os.path.isfile(path): files.append(path)
 
     if not files:
         return []
diff --git a/runtime/bin/builtin.cc b/runtime/bin/builtin.cc
index a18ca5644f8..326279a513e 100644
--- a/runtime/bin/builtin.cc
+++ b/runtime/bin/builtin.cc
@@ -22,14 +22,9 @@ Builtin::builtin_lib_props Builtin::builtin_libraries_[] = {
     // End marker.
     {NULL, false}};
 
-Dart_Port Builtin::load_port_ = ILLEGAL_PORT;
 const int Builtin::num_libs_ =
     sizeof(Builtin::builtin_libraries_) / sizeof(Builtin::builtin_lib_props);
 
-Dart_Handle Builtin::PartSource(BuiltinLibraryId id, const char* part_uri) {
-  UNREACHABLE();
-}
-
 void Builtin::SetNativeResolver(BuiltinLibraryId id) {
   ASSERT(static_cast<int>(id) >= 0);
   ASSERT(static_cast<int>(id) < num_libs_);
@@ -45,19 +40,6 @@ void Builtin::SetNativeResolver(BuiltinLibraryId id) {
   }
 }
 
-Builtin::BuiltinLibraryId Builtin::FindId(const char* url_string) {
-  int id = 0;
-  while (true) {
-    if (builtin_libraries_[id].url_ == NULL) {
-      return kInvalidLibrary;
-    }
-    if (strcmp(url_string, builtin_libraries_[id].url_) == 0) {
-      return static_cast<BuiltinLibraryId>(id);
-    }
-    id++;
-  }
-}
-
 Dart_Handle Builtin::LoadAndCheckLibrary(BuiltinLibraryId id) {
   ASSERT(static_cast<int>(id) >= 0);
   ASSERT(static_cast<int>(id) < num_libs_);
diff --git a/runtime/bin/builtin.h b/runtime/bin/builtin.h
index bfe08d0116c..7605fa0fd73 100644
--- a/runtime/bin/builtin.h
+++ b/runtime/bin/builtin.h
@@ -33,25 +33,13 @@ class Builtin {
     kCLILibrary,
   };
 
-  // Get source of part file specified in 'uri'.
-  static Dart_Handle PartSource(BuiltinLibraryId id, const char* part_uri);
-
   // Setup native resolver method built in library specified in 'id'.
   static void SetNativeResolver(BuiltinLibraryId id);
 
-  static BuiltinLibraryId FindId(const char* url_string);
-
   // Check if built in library specified in 'id' is already loaded, if not
   // load it.
   static Dart_Handle LoadAndCheckLibrary(BuiltinLibraryId id);
 
-  static Dart_Handle SetLoadPort(Dart_Port port);
-
-  static Dart_Port LoadPort() {
-    ASSERT(load_port_ != ILLEGAL_PORT);
-    return load_port_;
-  }
-
  private:
   // Native method support.
   static Dart_NativeFunction NativeLookup(Dart_Handle name,
@@ -60,7 +48,6 @@ class Builtin {
 
   static const uint8_t* NativeSymbol(Dart_NativeFunction nf);
 
-  static Dart_Port load_port_;
   static const int num_libs_;
 
   typedef struct {
diff --git a/runtime/bin/builtin_common.cc b/runtime/bin/builtin_common.cc
deleted file mode 100644
index 064d0048565..00000000000
--- a/runtime/bin/builtin_common.cc
+++ /dev/null
@@ -1,52 +0,0 @@
-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-#include <stdio.h>
-
-#include "include/dart_api.h"
-
-#include "bin/builtin.h"
-#include "bin/dartutils.h"
-#include "bin/platform.h"
-
-// Return the error from the containing function if handle is in error handle.
-#define RETURN_IF_ERROR(handle)                                                \
-  {                                                                            \
-    Dart_Handle __handle = handle;                                             \
-    if (Dart_IsError((__handle))) {                                            \
-      return __handle;                                                         \
-    }                                                                          \
-  }
-
-namespace dart {
-namespace bin {
-
-Dart_Handle Builtin::SetLoadPort(Dart_Port port) {
-  Dart_Handle builtin_lib =
-      Builtin::LoadAndCheckLibrary(Builtin::kBuiltinLibrary);
-  RETURN_IF_ERROR(builtin_lib);
-  // Set the _isolateId field.
-  Dart_Handle result =
-      Dart_SetField(builtin_lib, DartUtils::NewString("_isolateId"),
-                    Dart_NewInteger(Dart_GetMainPortId()));
-  RETURN_IF_ERROR(result);
-  load_port_ = port;
-  ASSERT(load_port_ != ILLEGAL_PORT);
-  Dart_Handle field_name = DartUtils::NewString("_loadPort");
-  RETURN_IF_ERROR(field_name);
-  Dart_Handle send_port = Dart_GetField(builtin_lib, field_name);
-  RETURN_IF_ERROR(send_port);
-  if (!Dart_IsNull(send_port)) {
-    // Already created and set.
-    return Dart_True();
-  }
-  send_port = Dart_NewSendPort(load_port_);
-  RETURN_IF_ERROR(send_port);
-  result = Dart_SetField(builtin_lib, field_name, send_port);
-  RETURN_IF_ERROR(result);
-  return Dart_True();
-}
-
-}  // namespace bin
-}  // namespace dart
diff --git a/runtime/bin/builtin_impl_sources.gni b/runtime/bin/builtin_impl_sources.gni
index f329f034055..97fcb968d28 100644
--- a/runtime/bin/builtin_impl_sources.gni
+++ b/runtime/bin/builtin_impl_sources.gni
@@ -15,7 +15,6 @@ builtin_impl_sources = [
   "crypto_linux.cc",
   "crypto_macos.cc",
   "crypto_win.cc",
-  "builtin_common.cc",
   "dartutils.cc",
   "dartutils.h",
   "directory.cc",
diff --git a/runtime/bin/dartutils.cc b/runtime/bin/dartutils.cc
index 4331e19f107..be84119bdc1 100644
--- a/runtime/bin/dartutils.cc
+++ b/runtime/bin/dartutils.cc
@@ -208,7 +208,7 @@ bool DartUtils::IsHttpSchemeURL(const char* url_name) {
 
 bool DartUtils::IsDartExtensionSchemeURL(const char* url_name) {
   static const intptr_t kDartExtensionSchemeLen = strlen(kDartExtensionScheme);
-  // If the URL starts with "dartext:" then it is considered as a special
+  // If the URL starts with "dart-ext:" then it is considered as a special
   // extension library URL which is handled differently from other URLs.
   return (strncmp(url_name, kDartExtensionScheme, kDartExtensionSchemeLen) ==
           0);
@@ -514,16 +514,6 @@ Dart_Handle DartUtils::PrepareCLILibrary(Dart_Handle cli_lib) {
                        wait_for_event_handle);
 }
 
-Dart_Handle DartUtils::SetupServiceLoadPort() {
-  // Wait for the service isolate to initialize the load port.
-  Dart_Port load_port = Dart_ServiceWaitForLoadPort();
-  if (load_port == ILLEGAL_PORT) {
-    return Dart_NewUnhandledExceptionError(
-        NewDartUnsupportedError("Service did not return load port."));
-  }
-  return Builtin::SetLoadPort(load_port);
-}
-
 Dart_Handle DartUtils::SetupPackageConfig(const char* packages_config) {
   Dart_Handle result = Dart_Null();
 
diff --git a/runtime/bin/dartutils.h b/runtime/bin/dartutils.h
index 10cfa711082..a0744ab9fd0 100644
--- a/runtime/bin/dartutils.h
+++ b/runtime/bin/dartutils.h
@@ -151,7 +151,6 @@ class DartUtils {
   static Dart_Handle MakeUint8Array(const uint8_t* buffer, intptr_t length);
   static Dart_Handle PrepareForScriptLoading(bool is_service_isolate,
                                              bool trace_loading);
-  static Dart_Handle SetupServiceLoadPort();
   static Dart_Handle SetupPackageConfig(const char* packages_file);
 
   static Dart_Handle SetupIOLibrary(const char* namespc_path,
diff --git a/runtime/bin/loader.cc b/runtime/bin/loader.cc
index c85712713e0..433e1f2cafa 100644
--- a/runtime/bin/loader.cc
+++ b/runtime/bin/loader.cc
@@ -19,237 +19,35 @@
 namespace dart {
 namespace bin {
 
-// Development flag.
-static bool trace_loader = false;
 #if !defined(DART_PRECOMPILED_RUNTIME)
 extern DFE dfe;
 #endif
 
-// Keep in sync with loader.dart.
-static const intptr_t _Dart_kInitLoader = 4;
-static const intptr_t _Dart_kImportExtension = 9;
+void Loader::InitForSnapshot(const char* snapshot_uri,
+                             IsolateData* isolate_data) {
+  ASSERT(isolate_data != NULL);
 
-Loader::Loader(IsolateData* isolate_data)
-    : port_(ILLEGAL_PORT),
-      isolate_data_(isolate_data),
-      error_(Dart_Null()),
-      monitor_(),
-      pending_operations_(0),
-      results_(NULL),
-      results_length_(0),
-      results_capacity_(0),
-      payload_(NULL),
-      payload_length_(0) {
-  ASSERT(isolate_data_ != NULL);
-  port_ = Dart_NewNativePort("Loader", Loader::NativeMessageHandler, false);
-  isolate_data_->set_loader(this);
-  AddLoader(port_, isolate_data_);
+  Dart_Handle result =
+      Loader::Init(isolate_data->packages_file(),
+                   DartUtils::original_working_directory, snapshot_uri);
+  ASSERT(!Dart_IsError(result));
 }
 
-Loader::~Loader() {
-  ASSERT(port_ != ILLEGAL_PORT);
-  // Enter the monitor while we close the Dart port. After the Dart port is
-  // closed, no more results can be queued.
-  monitor_.Enter();
-  Dart_CloseNativePort(port_);
-  monitor_.Exit();
-  RemoveLoader(port_);
-  port_ = ILLEGAL_PORT;
-  isolate_data_->set_loader(NULL);
-  isolate_data_ = NULL;
-  for (intptr_t i = 0; i < results_length_; i++) {
-    results_[i].Cleanup();
-  }
-  free(results_);
-  results_ = NULL;
-  payload_ = NULL;
-  payload_length_ = 0;
-}
-
-// Copy the contents of |message| into an |IOResult|.
-void Loader::IOResult::Setup(Dart_CObject* message) {
-  ASSERT(message->type == Dart_CObject_kArray);
-  ASSERT(message->value.as_array.length == 5);
-  Dart_CObject* tag_message = message->value.as_array.values[0];
-  ASSERT(tag_message != NULL);
-  Dart_CObject* uri_message = message->value.as_array.values[1];
-  ASSERT(uri_message != NULL);
-  Dart_CObject* resolved_uri_message = message->value.as_array.values[2];
-  ASSERT(resolved_uri_message != NULL);
-  Dart_CObject* library_uri_message = message->value.as_array.values[3];
-  ASSERT(library_uri_message != NULL);
-  Dart_CObject* payload_message = message->value.as_array.values[4];
-  ASSERT(payload_message != NULL);
-
-  // Grab the tag.
-  ASSERT(tag_message->type == Dart_CObject_kInt32);
-  tag = tag_message->value.as_int32;
-
-  // Grab the uri id.
-  ASSERT(uri_message->type == Dart_CObject_kString);
-  uri = strdup(uri_message->value.as_string);
-
-  // Grab the resolved uri.
-  ASSERT(resolved_uri_message->type == Dart_CObject_kString);
-  resolved_uri = strdup(resolved_uri_message->value.as_string);
-
-  // Grab the library uri if one is present.
-  if (library_uri_message->type != Dart_CObject_kNull) {
-    ASSERT(library_uri_message->type == Dart_CObject_kString);
-    library_uri = strdup(library_uri_message->value.as_string);
-  } else {
-    library_uri = NULL;
-  }
-
-  // Grab the payload.
-  if (payload_message->type == Dart_CObject_kString) {
-    // Payload is an error message.
-    payload_length = strlen(payload_message->value.as_string);
-    payload =
-        reinterpret_cast<uint8_t*>(strdup(payload_message->value.as_string));
-  } else {
-    // Payload is the contents of a file.
-    ASSERT(payload_message->type == Dart_CObject_kTypedData);
-    ASSERT(payload_message->value.as_typed_data.type == Dart_TypedData_kUint8);
-    payload_length = payload_message->value.as_typed_data.length;
-    payload = reinterpret_cast<uint8_t*>(malloc(payload_length));
-    memmove(payload, payload_message->value.as_typed_data.values,
-            payload_length);
-  }
-}
-
-void Loader::IOResult::Cleanup() {
-  free(uri);
-  free(resolved_uri);
-  free(library_uri);
-  free(payload);
-}
-
-// Send the Loader Initialization message to the service isolate. This
-// message is sent the first time a loader is constructed for an isolate and
-// seeds the service isolate with some initial state about this isolate.
-void Loader::Init(const char* package_root,
-                  const char* packages_file,
-                  const char* working_directory,
-                  const char* root_script_uri) {
-  // This port delivers loading messages to the service isolate.
-  Dart_Port loader_port = Builtin::LoadPort();
-  ASSERT(loader_port != ILLEGAL_PORT);
-
-  Dart_Handle request = Dart_NewList(9);
-  Dart_ListSetAt(request, 0, trace_loader ? Dart_True() : Dart_False());
-  Dart_ListSetAt(request, 1, Dart_NewInteger(Dart_GetMainPortId()));
-  Dart_ListSetAt(request, 2, Dart_NewInteger(_Dart_kInitLoader));
-  Dart_ListSetAt(request, 3, Dart_NewSendPort(port_));
-  Dart_ListSetAt(request, 4,
-                 (package_root == NULL)
+// Initialize package resolution state.
+Dart_Handle Loader::Init(const char* packages_file,
+                         const char* working_directory,
+                         const char* root_script_uri) {
+  const int kNumArgs = 3;
+  Dart_Handle dart_args[kNumArgs];
+  dart_args[0] = (packages_file == NULL)
                      ? Dart_Null()
-                     : Dart_NewStringFromCString(package_root));
-  Dart_ListSetAt(request, 5,
-                 (packages_file == NULL)
+                     : Dart_NewStringFromCString(packages_file);
+  dart_args[1] = Dart_NewStringFromCString(working_directory);
+  dart_args[2] = (root_script_uri == NULL)
                      ? Dart_Null()
-                     : Dart_NewStringFromCString(packages_file));
-  Dart_ListSetAt(request, 6, Dart_NewStringFromCString(working_directory));
-  Dart_ListSetAt(request, 7,
-                 (root_script_uri == NULL)
-                     ? Dart_Null()
-                     : Dart_NewStringFromCString(root_script_uri));
-  Dart_ListSetAt(request, 8, Dart_NewBoolean(Dart_IsReloading()));
-
-  bool success = Dart_Post(loader_port, request);
-  ASSERT(success);
-}
-
-void Loader::SendImportExtensionRequest(Dart_Handle url,
-                                        Dart_Handle library_url) {
-  // This port delivers loading messages to the service isolate.
-  Dart_Port loader_port = Builtin::LoadPort();
-  ASSERT(loader_port != ILLEGAL_PORT);
-
-  Dart_Handle request = Dart_NewList(6);
-  Dart_ListSetAt(request, 0, trace_loader ? Dart_True() : Dart_False());
-  Dart_ListSetAt(request, 1, Dart_NewInteger(Dart_GetMainPortId()));
-  Dart_ListSetAt(request, 2, Dart_NewInteger(_Dart_kImportExtension));
-  Dart_ListSetAt(request, 3, Dart_NewSendPort(port_));
-
-  Dart_ListSetAt(request, 4, url);
-  Dart_ListSetAt(request, 5, library_url);
-
-  if (Dart_Post(loader_port, request)) {
-    MonitorLocker ml(&monitor_);
-    pending_operations_++;
-  }
-}
-
-// Forward a request from the tag handler to the service isolate.
-void Loader::SendRequest(intptr_t tag,
-                         Dart_Handle url,
-                         Dart_Handle library_url) {
-  // This port delivers loading messages to the service isolate.
-  Dart_Port loader_port = Builtin::LoadPort();
-  ASSERT(loader_port != ILLEGAL_PORT);
-
-  Dart_Handle request = Dart_NewList(6);
-  Dart_ListSetAt(request, 0, trace_loader ? Dart_True() : Dart_False());
-  Dart_ListSetAt(request, 1, Dart_NewInteger(Dart_GetMainPortId()));
-  Dart_ListSetAt(request, 2, Dart_NewInteger(tag));
-  Dart_ListSetAt(request, 3, Dart_NewSendPort(port_));
-
-  Dart_ListSetAt(request, 4, url);
-  Dart_ListSetAt(request, 5, library_url);
-
-  if (Dart_Post(loader_port, request)) {
-    MonitorLocker ml(&monitor_);
-    pending_operations_++;
-  }
-}
-
-void Loader::QueueMessage(Dart_CObject* message) {
-  MonitorLocker ml(&monitor_);
-  if (results_length_ == results_capacity_) {
-    // Grow to an initial capacity or double in size.
-    results_capacity_ = (results_capacity_ == 0) ? 4 : results_capacity_ * 2;
-    results_ = reinterpret_cast<IOResult*>(
-        realloc(results_, sizeof(IOResult) * results_capacity_));
-    ASSERT(results_ != NULL);
-  }
-  ASSERT(results_ != NULL);
-  ASSERT(results_length_ < results_capacity_);
-  results_[results_length_].Setup(message);
-  results_length_++;
-  ml.Notify();
-}
-
-void Loader::BlockUntilComplete(ProcessResult process_result) {
-  MonitorLocker ml(&monitor_);
-
-  while (true) {
-    // If |ProcessQueueLocked| returns false, we've hit an error and should
-    // stop loading.
-    if (!ProcessQueueLocked(process_result)) {
-      break;
-    }
-
-    // When |pending_operations_| hits 0, we are done loading.
-    if (pending_operations_ == 0) {
-      break;
-    }
-
-    // Wait to be notified about new I/O results.
-    ml.Wait();
-  }
-}
-
-static bool LibraryHandleError(Dart_Handle library, Dart_Handle error) {
-  if (!Dart_IsNull(library) && !Dart_IsError(library)) {
-    ASSERT(Dart_IsLibrary(library));
-    Dart_Handle res = Dart_LibraryHandleError(library, error);
-    if (Dart_IsNull(res)) {
-      // Error was handled by library.
-      return true;
-    }
-  }
-  return false;
+                     : Dart_NewStringFromCString(root_script_uri);
+  return Dart_Invoke(DartUtils::LookupBuiltinLib(),
+                     DartUtils::NewString("_Init"), kNumArgs, dart_args);
 }
 
 static bool PathContainsSeparator(const char* path) {
@@ -258,156 +56,47 @@ static bool PathContainsSeparator(const char* path) {
           (strstr(path, File::PathSeparator()) != NULL));
 }
 
-class ScopedDecompress : public ValueObject {
- public:
-  ScopedDecompress(const uint8_t** payload, intptr_t* payload_length)
-      : payload_(payload),
-        payload_length_(payload_length),
-        decompressed_(NULL) {
-    DartUtils::MagicNumber payload_type =
-        DartUtils::SniffForMagicNumber(*payload, *payload_length);
-    if (payload_type == DartUtils::kGzipMagicNumber) {
-      int64_t start = Dart_TimelineGetMicros();
-      intptr_t decompressed_length = 0;
-      Decompress(*payload, *payload_length, &decompressed_,
-                 &decompressed_length);
-      int64_t end = Dart_TimelineGetMicros();
-      Dart_TimelineEvent("Decompress", start, end, Dart_Timeline_Event_Duration,
-                         0, NULL, NULL);
-      *payload_ = decompressed_;
-      *payload_length_ = decompressed_length;
-    }
-  }
-
-  ~ScopedDecompress() {
-    if (decompressed_ != NULL) {
-      free(decompressed_);
-    }
-  }
-
- private:
-  const uint8_t** payload_;
-  intptr_t* payload_length_;
-  uint8_t* decompressed_;
-};
-
-bool Loader::ProcessResultLocked(Loader* loader, Loader::IOResult* result) {
-  // We have to copy everything we care about out of |result| because after
-  // dropping the lock below |result| may no longer valid.
-  Dart_Handle uri =
-      Dart_NewStringFromCString(reinterpret_cast<char*>(result->uri));
-  Dart_Handle library_uri = Dart_Null();
-  if (result->library_uri != NULL) {
-    library_uri =
-        Dart_NewStringFromCString(reinterpret_cast<char*>(result->library_uri));
-  }
-
-  // A negative result tag indicates a loading error occurred in the service
-  // isolate. The payload is a C string of the error message.
-  if (result->tag < 0) {
-    Dart_Handle library = Dart_LookupLibrary(uri);
-    Dart_Handle error =
-        Dart_NewStringFromUTF8(result->payload, result->payload_length);
-    // If a library with the given uri exists, give it a chance to handle
-    // the error.
-    if (LibraryHandleError(library, error)) {
-      return true;
-    }
-    // Fall through
-    loader->error_ = Dart_NewUnhandledExceptionError(error);
-    return false;
-  }
-
-  if (result->tag == _Dart_kImportExtension) {
-    ASSERT(library_uri != Dart_Null());
-    Dart_Handle library = Dart_LookupLibrary(library_uri);
-    ASSERT(!Dart_IsError(library));
-    const char* lib_uri = reinterpret_cast<const char*>(result->payload);
-    if (strncmp(lib_uri, "http://", 7) == 0 ||
-        strncmp(lib_uri, "https://", 8) == 0) {
-      loader->error_ = Dart_NewApiError(
-          "Cannot load native extensions over http: or https:");
-      return false;
-    }
-    const char* extension_uri = reinterpret_cast<const char*>(result->uri);
-    const char* lib_path = NULL;
-    if (strncmp(lib_uri, "file://", 7) == 0) {
-      lib_path = DartUtils::RemoveScheme(lib_uri);
-    } else {
-      lib_path = lib_uri;
-    }
-    const char* extension_path = DartUtils::RemoveScheme(extension_uri);
-    if (!File::IsAbsolutePath(extension_path) &&
-        PathContainsSeparator(extension_path)) {
-      loader->error_ = DartUtils::NewError(
-          "Native extension path must be absolute, or simply the file name: %s",
-          extension_path);
-      return false;
-    }
-    Dart_Handle result =
-        Extensions::LoadExtension(lib_path, extension_path, library);
-    if (Dart_IsError(result)) {
-      loader->error_ = result;
-      return false;
-    }
-    return true;
-  }
-
-  // Check for payload and load accordingly.
-  const uint8_t* payload = result->payload;
-  intptr_t payload_length = result->payload_length;
-
-  // Decompress if gzip'd.
-  ScopedDecompress decompress(&payload, &payload_length);
-
-  const DartUtils::MagicNumber payload_type =
-      DartUtils::SniffForMagicNumber(payload, payload_length);
-  Dart_Handle source = Dart_Null();
-  if (payload_type == DartUtils::kUnknownMagicNumber) {
-    source = Dart_NewStringFromUTF8(payload, payload_length);
-    if (Dart_IsError(source)) {
-      loader->error_ =
-          DartUtils::NewError("%s is not a valid UTF-8 script",
-                              reinterpret_cast<char*>(result->uri));
-      return false;
-    }
-  }
-
-  UNREACHABLE();
-  return false;
-}
-
-bool Loader::ProcessQueueLocked(ProcessResult process_result) {
-  bool hit_error = false;
-  for (intptr_t i = 0; i < results_length(); i++) {
-    if (!hit_error) {
-      hit_error = !(*process_result)(this, &results_[i]);
-    }
-    pending_operations_--;
-    ASSERT(hit_error || (pending_operations_ >= 0));
-    results_[i].Cleanup();
-  }
-  results_length_ = 0;
-  return !hit_error;
-}
-
-void Loader::InitForSnapshot(const char* snapshot_uri,
-                             IsolateData* isolate_data) {
-  ASSERT(isolate_data != NULL);
-  ASSERT(!isolate_data->HasLoader());
-  // Setup a loader. The constructor does a bunch of leg work.
-  Loader* loader = new Loader(isolate_data);
-  // Send the init message.
-  loader->Init(isolate_data->isolate_group_data()->package_root,
-               isolate_data->packages_file(),
-               DartUtils::original_working_directory, snapshot_uri);
-  // Destroy the loader. The destructor does a bunch of leg work.
-  delete loader;
-}
-
 #define RETURN_ERROR(result)                                                   \
   if (Dart_IsError(result)) return result;
 
+Dart_Handle Loader::LoadImportExtension(const char* url_string,
+                                        Dart_Handle library) {
+  const char* lib_uri_str = NULL;
+  Dart_Handle lib_uri = Dart_LibraryResolvedUrl(library);
+  ASSERT(!Dart_IsError(lib_uri));
+  Dart_Handle result = Dart_StringToCString(lib_uri, &lib_uri_str);
+  RETURN_ERROR(result);
+
+  UriDecoder decoder(lib_uri_str);
+  lib_uri_str = decoder.decoded();
+
+  if (strncmp(lib_uri_str, "http://", 7) == 0 ||
+      strncmp(lib_uri_str, "https://", 8) == 0 ||
+      strncmp(lib_uri_str, "data://", 7) == 0) {
+    return DartUtils::NewError(
+        "Cannot load native extensions over http: or https: or data: %s",
+        lib_uri_str);
+  }
+
+  char* lib_path = NULL;
+  if (strncmp(lib_uri_str, "file://", 7) == 0) {
+    lib_path = DartUtils::DirName(lib_uri_str + 7);
+  } else {
+    lib_path = strdup(lib_uri_str);
+  }
+
+  const char* path = DartUtils::RemoveScheme(url_string);
+  if (!File::IsAbsolutePath(path) && PathContainsSeparator(path)) {
+    return DartUtils::NewError(
+        "Native extension path must be absolute, or simply the file name: %s",
+        path);
+  }
+
+  result = Extensions::LoadExtension(lib_path, path, library);
+  free(lib_path);
+  return result;
+}
+
 Dart_Handle Loader::ReloadNativeExtensions() {
   Dart_Handle scheme =
       Dart_NewStringFromCString(DartUtils::kDartExtensionScheme);
@@ -449,10 +138,6 @@ Dart_Handle Loader::ReloadNativeExtensions() {
   return Dart_True();
 }
 
-IsolateGroupData* Loader::isolate_group_data() {
-  return isolate_data_->isolate_group_data();
-}
-
 #if defined(DART_PRECOMPILED_RUNTIME)
 Dart_Handle Loader::LibraryTagHandler(Dart_LibraryTag tag,
                                       Dart_Handle library,
@@ -505,208 +190,38 @@ Dart_Handle Loader::LibraryTagHandler(Dart_LibraryTag tag,
     return result;
   }
   if (tag == Dart_kImportExtensionTag) {
-    if (strncmp(url_string, "dart-ext:", 9) != 0) {
+    if (!DartUtils::IsDartExtensionSchemeURL(url_string)) {
       return DartUtils::NewError(
-          "Native extensions must use the dart-ext: scheme.");
+          "Native extensions must use the dart-ext: scheme : %s", url_string);
     }
-    const char* path = DartUtils::RemoveScheme(url_string);
-
-    const char* lib_uri = NULL;
-    result = Dart_StringToCString(Dart_LibraryResolvedUrl(library), &lib_uri);
-    RETURN_ERROR(result);
-
-    UriDecoder decoder(lib_uri);
-    lib_uri = decoder.decoded();
-
-    char* lib_path = NULL;
-    if (strncmp(lib_uri, "file://", 7) == 0) {
-      lib_path = DartUtils::DirName(lib_uri + 7);
+    return Loader::LoadImportExtension(url_string, library);
+  }
+  if (dfe.CanUseDartFrontend() && dfe.UseDartFrontend() &&
+      (tag == Dart_kImportTag)) {
+    // E.g., IsolateMirror.loadUri.
+    char* error = NULL;
+    int exit_code = 0;
+    uint8_t* kernel_buffer = NULL;
+    intptr_t kernel_buffer_size = -1;
+    dfe.CompileAndReadScript(url_string, &kernel_buffer, &kernel_buffer_size,
+                             &error, &exit_code, NULL);
+    if (exit_code == 0) {
+      return Dart_LoadLibraryFromKernel(kernel_buffer, kernel_buffer_size);
+    } else if (exit_code == kCompilationErrorExitCode) {
+      Dart_Handle result = Dart_NewCompilationError(error);
+      free(error);
+      return result;
     } else {
-      lib_path = strdup(lib_uri);
-    }
-
-    if (!File::IsAbsolutePath(path) && PathContainsSeparator(path)) {
-      return DartUtils::NewError(
-          "Native extension path must be absolute, or simply the file name: "
-          "%s: ",
-          path);
-    }
-
-    Dart_Handle result = Extensions::LoadExtension(lib_path, path, library);
-    free(lib_path);
-    return result;
-  }
-  if (DartUtils::IsDartExtensionSchemeURL(url_string)) {
-    // Handle early error cases for dart-ext: imports.
-    if (tag != Dart_kImportTag) {
-      return DartUtils::NewError("Dart extensions must use import: '%s'",
-                                 url_string);
-    }
-    Dart_Handle library_url = Dart_LibraryUrl(library);
-    if (Dart_IsError(library_url)) {
-      return library_url;
+      Dart_Handle result = Dart_NewApiError(error);
+      free(error);
+      return result;
     }
   }
-
-  auto isolate_data = reinterpret_cast<IsolateData*>(Dart_CurrentIsolateData());
-  ASSERT(isolate_data != NULL);
-
-  // Grab this isolate's loader.
-  Loader* loader = NULL;
-
-  if (!isolate_data->HasLoader()) {
-    // The isolate doesn't have a loader -- this is the outer invocation which
-    // will block.
-
-    // Setup the loader. The constructor does a bunch of leg work.
-    loader = new Loader(isolate_data);
-    loader->Init(isolate_data->isolate_group_data()->package_root,
-                 isolate_data->packages_file(),
-                 DartUtils::original_working_directory, NULL);
-  } else {
-    // The isolate has a loader -- this is an inner invocation that will queue
-    // work with the service isolate.
-    // Use the existing loader.
-    loader = isolate_data->loader();
-  }
-  ASSERT(loader != NULL);
-  ASSERT(isolate_data->HasLoader());
-
-  if (DartUtils::IsDartExtensionSchemeURL(url_string)) {
-    loader->SendImportExtensionRequest(url, Dart_LibraryUrl(library));
-  } else {
-    if (dfe.CanUseDartFrontend() && dfe.UseDartFrontend() &&
-        (tag == Dart_kImportTag)) {
-      // E.g., IsolateMirror.loadUri.
-      char* error = NULL;
-      int exit_code = 0;
-      uint8_t* kernel_buffer = NULL;
-      intptr_t kernel_buffer_size = -1;
-      dfe.CompileAndReadScript(url_string, &kernel_buffer, &kernel_buffer_size,
-                               &error, &exit_code, NULL);
-      if (exit_code == 0) {
-        return Dart_LoadLibraryFromKernel(kernel_buffer, kernel_buffer_size);
-      } else if (exit_code == kCompilationErrorExitCode) {
-        Dart_Handle result = Dart_NewCompilationError(error);
-        free(error);
-        return result;
-      } else {
-        Dart_Handle result = Dart_NewApiError(error);
-        free(error);
-        return result;
-      }
-    } else {
-      loader->SendRequest(
-          tag, url,
-          (library != Dart_Null()) ? Dart_LibraryUrl(library) : Dart_Null());
-    }
-  }
-
-  // The outer invocation of the tag handler will block here until all nested
-  // invocations complete.
-  loader->BlockUntilComplete(ProcessResultLocked);
-
-  // Remember the error (if any).
-  Dart_Handle error = loader->error();
-  // Destroy the loader. The destructor does a bunch of leg work.
-  delete loader;
-
-  // An error occurred during loading.
-  if (!Dart_IsNull(error)) {
-    // We got an error during loading, return the error to the caller.
-    return error;
-  }
-
-  // Finalize loading.
-  error = Dart_FinalizeLoading(true);
-  if (Dart_IsError(error)) {
-    return error;
-  }
-  return Dart_Null();
+  return DartUtils::NewError("Invalid tag : %d '%s'", tag, url_string);
 }
 #endif  // !defined(DART_PRECOMPILED_RUNTIME)
 
 void Loader::InitOnce() {
-  loader_infos_lock_ = new Mutex();
-}
-
-Mutex* Loader::loader_infos_lock_;
-Loader::LoaderInfo* Loader::loader_infos_ = NULL;
-intptr_t Loader::loader_infos_length_ = 0;
-intptr_t Loader::loader_infos_capacity_ = 0;
-
-// Add a mapping from |port| to |isolate_data| (really the loader). When a
-// native message arrives, we use this map to report the I/O result to the
-// correct loader.
-// This happens whenever an isolate begins loading.
-void Loader::AddLoader(Dart_Port port, IsolateData* isolate_data) {
-  MutexLocker ml(loader_infos_lock_);
-  ASSERT(LoaderForLocked(port) == NULL);
-  if (loader_infos_length_ == loader_infos_capacity_) {
-    // Grow to an initial capacity or double in size.
-    loader_infos_capacity_ =
-        (loader_infos_capacity_ == 0) ? 4 : loader_infos_capacity_ * 2;
-    loader_infos_ = reinterpret_cast<Loader::LoaderInfo*>(realloc(
-        loader_infos_, sizeof(Loader::LoaderInfo) * loader_infos_capacity_));
-    ASSERT(loader_infos_ != NULL);
-    // Initialize new entries.
-    for (intptr_t i = loader_infos_length_; i < loader_infos_capacity_; i++) {
-      loader_infos_[i].port = ILLEGAL_PORT;
-      loader_infos_[i].isolate_data = NULL;
-    }
-  }
-  ASSERT(loader_infos_length_ < loader_infos_capacity_);
-  loader_infos_[loader_infos_length_].port = port;
-  loader_infos_[loader_infos_length_].isolate_data = isolate_data;
-  loader_infos_length_++;
-  ASSERT(LoaderForLocked(port) != NULL);
-}
-
-// Remove |port| from the map.
-// This happens once an isolate has finished loading.
-void Loader::RemoveLoader(Dart_Port port) {
-  MutexLocker ml(loader_infos_lock_);
-  const intptr_t index = LoaderIndexFor(port);
-  ASSERT(index >= 0);
-  const intptr_t last = loader_infos_length_ - 1;
-  ASSERT(last >= 0);
-  if (index != last) {
-    // Swap with the tail.
-    loader_infos_[index] = loader_infos_[last];
-  }
-  loader_infos_length_--;
-}
-
-intptr_t Loader::LoaderIndexFor(Dart_Port port) {
-  for (intptr_t i = 0; i < loader_infos_length_; i++) {
-    if (loader_infos_[i].port == port) {
-      return i;
-    }
-  }
-  return -1;
-}
-
-Loader* Loader::LoaderForLocked(Dart_Port port) {
-  intptr_t index = LoaderIndexFor(port);
-  if (index < 0) {
-    return NULL;
-  }
-  return loader_infos_[index].isolate_data->loader();
-}
-
-Loader* Loader::LoaderFor(Dart_Port port) {
-  MutexLocker ml(loader_infos_lock_);
-  return LoaderForLocked(port);
-}
-
-void Loader::NativeMessageHandler(Dart_Port dest_port_id,
-                                  Dart_CObject* message) {
-  MutexLocker ml(loader_infos_lock_);
-  Loader* loader = LoaderForLocked(dest_port_id);
-  if (loader == NULL) {
-    return;
-  }
-  loader->QueueMessage(message);
 }
 
 }  // namespace bin
diff --git a/runtime/bin/loader.h b/runtime/bin/loader.h
index 54af63fa1ac..bb2576dc14c 100644
--- a/runtime/bin/loader.h
+++ b/runtime/bin/loader.h
@@ -17,9 +17,6 @@ namespace bin {
 
 class Loader {
  public:
-  explicit Loader(IsolateData* isolate_data);
-  ~Loader();
-
   static void InitForSnapshot(const char* snapshot_uri,
                               IsolateData* isolate_data);
 
@@ -30,101 +27,18 @@ class Loader {
                                        Dart_Handle library,
                                        Dart_Handle url);
 
-  IsolateGroupData* isolate_group_data();
-
-  Dart_Handle error() const { return error_; }
-
   static void InitOnce();
 
  private:
-  // The port assigned to our native message handler.
-  Dart_Port port_;
-  // Each Loader is associated with an Isolate via its IsolateData.
-  IsolateData* isolate_data_;
-  // Remember the first error that occurs during loading.
-  Dart_Handle error_;
-  // This monitor is used to protect the pending operations count and the
-  // I/O result queue.
-  Monitor monitor_;
+  static Dart_Handle Init(const char* packages_file,
+                          const char* working_directory,
+                          const char* root_script_uri);
 
-  // The number of operations dispatched to the service isolate for loading.
-  // Must be accessed with monitor_ held.
-  intptr_t pending_operations_;
+  static Dart_Handle LoadImportExtension(const char* url_string,
+                                         Dart_Handle library);
 
-  // The result of an I/O request to the service isolate. Payload is either
-  // a UInt8Array or a C string containing an error message.
-  struct IOResult {
-    uint8_t* payload;
-    intptr_t payload_length;
-    char* library_uri;
-    char* uri;
-    char* resolved_uri;
-    int8_t tag;
-
-    void Setup(Dart_CObject* message);
-    void Cleanup();
-  };
-  // An array of I/O results queued from the service isolate.
-  IOResult* results_;
-  intptr_t results_length_;
-  intptr_t results_capacity_;
-  uint8_t* payload_;
-  intptr_t payload_length_;
-  typedef bool (*ProcessResult)(Loader* loader, IOResult* result);
-
-  intptr_t results_length() {
-    return *static_cast<volatile intptr_t*>(&results_length_);
-  }
-
-  // Send the loader init request to the service isolate.
-  void Init(const char* package_root,
-            const char* packages_file,
-            const char* working_directory,
-            const char* root_script_uri);
-
-  // Send a request for a dart-ext: import to the service isolate.
-  void SendImportExtensionRequest(Dart_Handle url, Dart_Handle library_url);
-
-  // Send a request from the tag handler to the service isolate.
-  void SendRequest(intptr_t tag, Dart_Handle url, Dart_Handle library_url);
-
-  /// Queue |message| and notify the loader that a message is available.
-  void QueueMessage(Dart_CObject* message);
-
-  /// Blocks the caller until the loader is finished.
-  void BlockUntilComplete(ProcessResult process_result);
-
-  /// Returns false if |result| is an error and the loader should quit.
-  static bool ProcessResultLocked(Loader* loader, IOResult* result);
-
-  /// Returns false if an error occurred and the loader should quit.
-  bool ProcessQueueLocked(ProcessResult process_result);
-
-  // We use one native message handler callback for N loaders. The native
-  // message handler callback provides us with the Dart_Port which we use as a
-  // key into our map of active loaders from |port| to |isolate_data|.
-
-  // Static information to map Dart_Port back to the isolate in question.
-  struct LoaderInfo {
-    Dart_Port port;
-    IsolateData* isolate_data;
-  };
-
-  // The map of active loaders.
-  static Mutex* loader_infos_lock_;
-  static LoaderInfo* loader_infos_;
-  static intptr_t loader_infos_length_;
-  static intptr_t loader_infos_capacity_;
-
-  static void AddLoader(Dart_Port port, IsolateData* data);
-  static void RemoveLoader(Dart_Port port);
-  static intptr_t LoaderIndexFor(Dart_Port port);
-  static Loader* LoaderFor(Dart_Port port);
-  static Loader* LoaderForLocked(Dart_Port port);
-
-  // This is the global callback for the native message handlers.
-  static void NativeMessageHandler(Dart_Port dest_port_id,
-                                   Dart_CObject* message);
+  DISALLOW_ALLOCATION();
+  DISALLOW_IMPLICIT_CONSTRUCTORS(Loader);
 };
 
 }  // namespace bin
diff --git a/runtime/bin/main.cc b/runtime/bin/main.cc
index 7678229a8a7..8225e8f3f2f 100644
--- a/runtime/bin/main.cc
+++ b/runtime/bin/main.cc
@@ -191,13 +191,6 @@ static Dart_Handle SetupCoreLibraries(Dart_Isolate isolate,
   result = DartUtils::PrepareForScriptLoading(false, Options::trace_loading());
   if (Dart_IsError(result)) return result;
 
-  if (Dart_IsVMFlagSet("support_service") || !Dart_IsPrecompiledRuntime()) {
-    // Set up the load port provided by the service isolate so that we can
-    // load scripts.
-    result = DartUtils::SetupServiceLoadPort();
-    if (Dart_IsError(result)) return result;
-  }
-
   // Setup packages config if specified.
   result = DartUtils::SetupPackageConfig(packages_file);
   if (Dart_IsError(result)) return result;
diff --git a/runtime/bin/vmservice/loader.dart b/runtime/bin/vmservice/loader.dart
deleted file mode 100644
index 35a5fdc5dbc..00000000000
--- a/runtime/bin/vmservice/loader.dart
+++ /dev/null
@@ -1,865 +0,0 @@
-// Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
-// for details. All rights reserved. Use of this source code is governed by a
-// BSD-style license that can be found in the LICENSE file.
-
-// @dart = 2.6
-
-part of vmservice_io;
-
-_sanitizeWindowsPath(path) {
-  // For Windows we need to massage the paths a bit according to
-  // http://blogs.msdn.com/b/ie/archive/2006/12/06/file-uris-in-windows.aspx
-  //
-  // Convert
-  // C:\one\two\three
-  // to
-  // /C:/one/two/three
-
-  if (_isWindows == false) {
-    // Do nothing when not running Windows.
-    return path;
-  }
-
-  var fixedPath = "${path.replaceAll('\\', '/')}";
-
-  if ((path.length > 2) && (path[1] == ':')) {
-    // Path begins with a drive letter.
-    return '/$fixedPath';
-  }
-
-  return fixedPath;
-}
-
-@pragma("vm:entry-point")
-bool _traceLoading = false;
-
-// State associated with the isolate that is used for loading.
-class IsolateLoaderState extends IsolateEmbedderData {
-  IsolateLoaderState(this.isolateId);
-
-  final int isolateId;
-  bool _dead = false;
-  SendPort sp;
-
-  void init(String packageRootFlag, String packagesConfigFlag,
-      String workingDirectory, String rootScript) {
-    if (_dead) {
-      return;
-    }
-    // _workingDirectory must be set first.
-    _workingDirectory = new Uri.directory(workingDirectory);
-    if (rootScript != null) {
-      _rootScript = Uri.parse(rootScript);
-    }
-    // If the --packages flag was passed.
-    if (packagesConfigFlag != null) {
-      _setPackagesConfig(packagesConfigFlag);
-    }
-  }
-
-  void updatePackageMap(String packagesConfigFlag) {
-    if (packagesConfigFlag == null) {
-      return;
-    }
-    _packageMap = null;
-    _setPackagesConfig(packagesConfigFlag);
-  }
-
-  void cleanup() {
-    _dead = true;
-    if (_packagesPort != null) {
-      _packagesPort.close();
-      _packagesPort = null;
-    }
-  }
-
-  // The working directory when the embedder started.
-  Uri _workingDirectory;
-
-  // The root script's uri.
-  Uri _rootScript;
-
-  // Packages are either resolved looking up in a map or resolved from within a
-  // package root.
-  bool get _packagesReady =>
-      (_packageRoot != null) ||
-      (_packageMap != null) ||
-      (_packageError != null);
-
-  // Error string set if there was an error resolving package configuration.
-  // For example not finding a .packages file or packages/ directory, malformed
-  // .packages file or any other related error.
-  String _packageError = null;
-
-  // The directory to look in to resolve "package:" scheme URIs. By default it
-  // is the 'packages' directory right next to the script.
-  Uri _packageRoot = null;
-
-  // The map describing how certain package names are mapped to Uris.
-  Uri _packageConfig = null;
-  Map<String, Uri> _packageMap = null;
-
-  _setPackagesConfig(String packagesParam) {
-    var packagesName = _sanitizeWindowsPath(packagesParam);
-    var packagesUri = Uri.parse(packagesName);
-    if (packagesUri.scheme == '') {
-      // Script does not have a scheme, assume that it is a path,
-      // resolve it against the working directory.
-      packagesUri = _workingDirectory.resolveUri(packagesUri);
-    }
-    _requestPackagesMap(packagesUri);
-    _pendingPackageLoads.add(() {
-      // Dummy action.
-    });
-  }
-
-  // Handling of access to the package root or package map from user code.
-  _triggerPackageResolution(action) {
-    if (_packagesReady) {
-      // Packages are ready. Execute the action now.
-      action();
-    } else {
-      if (_pendingPackageLoads.isEmpty) {
-        // Package resolution has not been setup yet, and this is the first
-        // request for package resolution & loading.
-        _requestPackagesMap();
-      }
-      // Register the action for when the package resolution is ready.
-      _pendingPackageLoads.add(action);
-    }
-  }
-
-  // A list of callbacks which should be invoked after the package map has been
-  // loaded.
-  List<Function> _pendingPackageLoads = [];
-
-  // Given a uri with a 'package' scheme, return a Uri that is prefixed with
-  // the package root or resolved relative to the package configuration.
-  Uri _resolvePackageUri(Uri uri) {
-    assert(uri.scheme == "package");
-    assert(_packagesReady);
-
-    if (uri.host.isNotEmpty) {
-      var path = '${uri.host}${uri.path}';
-      var right = 'package:$path';
-      var wrong = 'package://$path';
-
-      throw "URIs using the 'package:' scheme should look like "
-          "'$right', not '$wrong'.";
-    }
-
-    var packageNameEnd = uri.path.indexOf('/');
-    if (packageNameEnd == 0) {
-      // Package URIs must have a non-empty package name (not start with "/").
-      throw "URIS using the 'package:' scheme should look like "
-          "'package:packageName${uri.path}', not 'package:${uri.path}'";
-    }
-    if (_traceLoading) {
-      _log('Resolving package with uri path: ${uri.path}');
-    }
-    var resolvedUri;
-    if (_packageError != null) {
-      if (_traceLoading) {
-        _log("Resolving package with pending resolution error: $_packageError");
-      }
-      throw _packageError;
-    } else if (_packageRoot != null) {
-      resolvedUri = _packageRoot.resolve(uri.path);
-    } else {
-      if (packageNameEnd < 0) {
-        // Package URIs must have a path after the package name, even if it's
-        // just "/".
-        throw "URIS using the 'package:' scheme should look like "
-            "'package:${uri.path}/', not 'package:${uri.path}'";
-      }
-      var packageName = uri.path.substring(0, packageNameEnd);
-      var mapping = _packageMap[packageName];
-      if (_traceLoading) {
-        _log("Mapped '$packageName' package to '$mapping'");
-      }
-      if (mapping == null) {
-        throw "No mapping for '$packageName' package when resolving '$uri'.";
-      }
-      var path;
-      assert(uri.path.length > packageName.length);
-      path = uri.path.substring(packageName.length + 1);
-      if (_traceLoading) {
-        _log("Path to be resolved in package: $path");
-      }
-      resolvedUri = mapping.resolve(path);
-    }
-    if (_traceLoading) {
-      _log("Resolved '$uri' to '$resolvedUri'.");
-    }
-    return resolvedUri;
-  }
-
-  RawReceivePort _packagesPort;
-
-  void _requestPackagesMap([Uri packageConfig]) {
-    if (_packagesPort != null) {
-      // Already scheduled.
-      return;
-    }
-    // Create a port to receive the packages map on.
-    _packagesPort = new RawReceivePort(_handlePackagesReply);
-    var sp = _packagesPort.sendPort;
-
-    if (packageConfig != null) {
-      // Explicitly specified .packages path.
-      _handlePackagesRequest(sp, _traceLoading, -2, packageConfig);
-    } else {
-      // Search for .packages starting at the root script.
-      _handlePackagesRequest(sp, _traceLoading, -1, _rootScript);
-    }
-
-    if (_traceLoading) {
-      _log("Requested packages map for '$_rootScript'.");
-    }
-  }
-
-  void _handlePackagesReply(msg) {
-    if (_packagesPort == null) {
-      return;
-    }
-    // Make sure to close the _packagePort before any other action.
-    _packagesPort.close();
-    _packagesPort = null;
-
-    if (_traceLoading) {
-      _log("Got packages reply: $msg");
-    }
-    if (msg is String) {
-      if (_traceLoading) {
-        _log("Got failure response on package port: '$msg'");
-      }
-      // Remember the error message.
-      _packageError = msg;
-    } else if (msg is List) {
-      if (msg.length == 1) {
-        if (_traceLoading) {
-          _log("Received package root: '${msg[0]}'");
-        }
-        _packageRoot = Uri.parse(msg[0]);
-      } else {
-        // First entry contains the location of the loaded .packages file.
-        assert((msg.length % 2) == 0);
-        assert(msg.length >= 2);
-        assert(msg[1] == null);
-        _packageConfig = Uri.parse(msg[0]);
-        _packageMap = new Map<String, Uri>();
-        for (var i = 2; i < msg.length; i += 2) {
-          // TODO(iposva): Complain about duplicate entries.
-          _packageMap[msg[i]] = Uri.parse(msg[i + 1]);
-        }
-        if (_traceLoading) {
-          _log("Setup package map: $_packageMap");
-        }
-      }
-    } else {
-      _packageError = "Bad type of packages reply: ${msg.runtimeType}";
-      if (_traceLoading) {
-        _log(_packageError);
-      }
-    }
-
-    // Resolve all pending package loads now that we know how to resolve them.
-    while (_pendingPackageLoads.length > 0) {
-      // Order does not matter as we queue all of the requests up right now.
-      var req = _pendingPackageLoads.removeLast();
-      // Call the registered closure, to handle the delayed action.
-      req();
-    }
-    // Reset the pending package loads to empty. So that we eventually can
-    // finish loading.
-    _pendingPackageLoads = [];
-  }
-}
-
-_log(msg) {
-  print("% $msg");
-}
-
-var _httpClient;
-
-// Send a response to the requesting isolate.
-void _sendResourceResponse(SendPort sp, int tag, Uri uri, Uri resolvedUri,
-    String libraryUrl, dynamic data) {
-  assert((data is List<int>) || (data is String));
-  var msg = new List(5);
-  if (data is String) {
-    // We encountered an error, flip the sign of the tag to indicate that.
-    tag = -tag;
-    if (libraryUrl == null) {
-      data = 'Could not load "$uri": $data';
-    } else {
-      data = 'Could not import "$uri" from "$libraryUrl": $data';
-    }
-  }
-  msg[0] = tag;
-  msg[1] = uri.toString();
-  msg[2] = resolvedUri.toString();
-  msg[3] = libraryUrl;
-  msg[4] = data;
-  sp.send(msg);
-}
-
-// Send a response to the requesting isolate.
-void _sendExtensionImportResponse(
-    SendPort sp, Uri uri, String libraryUrl, String resolvedUri) {
-  var msg = new List(5);
-  int tag = _Dart_kImportExtension;
-  if (resolvedUri == null) {
-    // We could not resolve the dart-ext: uri.
-    tag = -tag;
-    resolvedUri = 'Could not resolve "$uri" from "$libraryUrl"';
-  }
-  msg[0] = tag;
-  msg[1] = uri.toString();
-  msg[2] = resolvedUri;
-  msg[3] = libraryUrl;
-  msg[4] = resolvedUri;
-  sp.send(msg);
-}
-
-// Handling of packages requests. Finding and parsing of .packages file or
-// packages/ directories.
-const _LF = 0x0A;
-const _CR = 0x0D;
-const _SPACE = 0x20;
-const _HASH = 0x23;
-const _DOT = 0x2E;
-const _COLON = 0x3A;
-const _DEL = 0x7F;
-
-const _invalidPackageNameChars = const [
-  true, //  space
-  false, // !
-  true, //  "
-  true, //  #
-  false, // $
-  true, //  %
-  false, // &
-  false, // '
-  false, // (
-  false, // )
-  false, // *
-  false, // +
-  false, // ,
-  false, // -
-  false, // .
-  true, //  /
-  false, // 0
-  false, // 1
-  false, // 2
-  false, // 3
-  false, // 4
-  false, // 5
-  false, // 6
-  false, // 7
-  false, // 8
-  false, // 9
-  true, //  :
-  false, // ;
-  true, //  <
-  false, // =
-  true, //  >
-  true, //  ?
-  false, // @
-  false, // A
-  false, // B
-  false, // C
-  false, // D
-  false, // E
-  false, // F
-  false, // G
-  false, // H
-  false, // I
-  false, // J
-  false, // K
-  false, // L
-  false, // M
-  false, // N
-  false, // O
-  false, // P
-  false, // Q
-  false, // R
-  false, // S
-  false, // T
-  false, // U
-  false, // V
-  false, // W
-  false, // X
-  false, // Y
-  false, // Z
-  true, //  [
-  true, //  \
-  true, //  ]
-  true, //  ^
-  false, // _
-  true, //  `
-  false, // a
-  false, // b
-  false, // c
-  false, // d
-  false, // e
-  false, // f
-  false, // g
-  false, // h
-  false, // i
-  false, // j
-  false, // k
-  false, // l
-  false, // m
-  false, // n
-  false, // o
-  false, // p
-  false, // q
-  false, // r
-  false, // s
-  false, // t
-  false, // u
-  false, // v
-  false, // w
-  false, // x
-  false, // y
-  false, // z
-  true, //  {
-  true, //  |
-  true, //  }
-  false, // ~
-  true, //  DEL
-];
-
-_parsePackagesFile(
-    SendPort sp, bool traceLoading, Uri packagesFile, List<int> data) {
-  // The first entry contains the location of the identified .packages file
-  // instead of a mapping.
-  var result = [packagesFile.toString(), null];
-  var index = 0;
-  var len = data.length;
-  while (index < len) {
-    var start = index;
-    var char = data[index];
-    if ((char == _CR) || (char == _LF)) {
-      // Skipping empty lines.
-      index++;
-      continue;
-    }
-
-    // Identify split within the line and end of the line.
-    var separator = -1;
-    var end = len;
-    // Verifying validity of package name while scanning the line.
-    var nonDot = false;
-    var invalidPackageName = false;
-
-    // Scan to the end of the line or data.
-    while (index < len) {
-      char = data[index++];
-      // If we have not reached the separator yet, determine whether we are
-      // scanning legal package name characters.
-      if (separator == -1) {
-        if ((char == _COLON)) {
-          // The first colon on a line is the separator between package name and
-          // related URI.
-          separator = index - 1;
-        } else {
-          // Still scanning the package name part. Check for the validity of
-          // the characters.
-          nonDot = nonDot || (char != _DOT);
-          invalidPackageName = invalidPackageName ||
-              (char < _SPACE) ||
-              (char > _DEL) ||
-              _invalidPackageNameChars[char - _SPACE];
-        }
-      }
-      // Identify end of line.
-      if ((char == _CR) || (char == _LF)) {
-        end = index - 1;
-        break;
-      }
-    }
-
-    // No further handling needed for comment lines.
-    if (data[start] == _HASH) {
-      if (traceLoading) {
-        _log("Skipping comment in $packagesFile:\n"
-            "${new String.fromCharCodes(data, start, end)}");
-      }
-      continue;
-    }
-
-    // Check for a badly formatted line, starting with a ':'.
-    if (separator == start) {
-      var line = new String.fromCharCodes(data, start, end);
-      if (traceLoading) {
-        _log("Line starts with ':' in $packagesFile:\n"
-            "$line");
-      }
-      sp.send("Missing package name in $packagesFile:\n"
-          "$line");
-      return;
-    }
-
-    // Ensure there is a separator on the line.
-    if (separator == -1) {
-      var line = new String.fromCharCodes(data, start, end);
-      if (traceLoading) {
-        _log("Line has no ':' in $packagesFile:\n"
-            "$line");
-      }
-      sp.send("Missing ':' separator in $packagesFile:\n"
-          "$line");
-      return;
-    }
-
-    var packageName = new String.fromCharCodes(data, start, separator);
-
-    // Check for valid package name.
-    if (invalidPackageName || !nonDot) {
-      var line = new String.fromCharCodes(data, start, end);
-      if (traceLoading) {
-        _log("Invalid package name $packageName in $packagesFile");
-      }
-      sp.send("Invalid package name '$packageName' in $packagesFile:\n"
-          "$line");
-      return;
-    }
-
-    if (traceLoading) {
-      _log("packageName: $packageName");
-    }
-    var packageUri = new String.fromCharCodes(data, separator + 1, end);
-    if (traceLoading) {
-      _log("original packageUri: $packageUri");
-    }
-    // Ensure the package uri ends with a /.
-    if (!packageUri.endsWith("/")) {
-      packageUri = "$packageUri/";
-    }
-    packageUri = packagesFile.resolve(packageUri).toString();
-    if (traceLoading) {
-      _log("mapping: $packageName -> $packageUri");
-    }
-    result.add(packageName);
-    result.add(packageUri);
-  }
-
-  if (traceLoading) {
-    _log("Parsed packages file at $packagesFile. Sending:\n$result");
-  }
-  sp.send(result);
-}
-
-_loadPackagesFile(SendPort sp, bool traceLoading, Uri packagesFile) async {
-  try {
-    var data = await new File.fromUri(packagesFile).readAsBytes();
-    if (traceLoading) {
-      _log("Loaded packages file from $packagesFile:\n"
-          "${new String.fromCharCodes(data)}");
-    }
-    _parsePackagesFile(sp, traceLoading, packagesFile, data);
-  } catch (e, s) {
-    if (traceLoading) {
-      _log("Error loading packages: $e\n$s");
-    }
-    sp.send("Uncaught error ($e) loading packages file.");
-  }
-}
-
-_findPackagesFile(SendPort sp, bool traceLoading, Uri base) async {
-  try {
-    // Walk up the directory hierarchy to check for the existence of
-    // .packages files in parent directories and for the existence of a
-    // packages/ directory on the first iteration.
-    var dir = new File.fromUri(base).parent;
-    var prev = null;
-    // Keep searching until we reach the root.
-    while ((prev == null) || (prev.path != dir.path)) {
-      // Check for the existence of a .packages file and if it exists try to
-      // load and parse it.
-      var dirUri = dir.uri;
-      var packagesFile = dirUri.resolve(".packages");
-      if (traceLoading) {
-        _log("Checking for $packagesFile file.");
-      }
-      var exists = await new File.fromUri(packagesFile).exists();
-      if (traceLoading) {
-        _log("$packagesFile exists: $exists");
-      }
-      if (exists) {
-        _loadPackagesFile(sp, traceLoading, packagesFile);
-        return;
-      }
-      // Move up one level.
-      prev = dir;
-      dir = dir.parent;
-    }
-
-    // No .packages file was found.
-    if (traceLoading) {
-      _log("Could not resolve a package location from $base");
-    }
-    sp.send("Could not resolve a package location for base at $base");
-  } catch (e, s) {
-    if (traceLoading) {
-      _log("Error loading packages: $e\n$s");
-    }
-    sp.send("Uncaught error ($e) loading packages file.");
-  }
-}
-
-Future<bool> _loadHttpPackagesFile(
-    SendPort sp, bool traceLoading, Uri resource) async {
-  try {
-    if (_httpClient == null) {
-      _httpClient = new HttpClient()..maxConnectionsPerHost = 6;
-    }
-    if (traceLoading) {
-      _log("Fetching packages file from '$resource'.");
-    }
-    var req = await _httpClient.getUrl(resource);
-    var rsp = await req.close();
-    var builder = new BytesBuilder(copy: false);
-    await for (var bytes in rsp) {
-      builder.add(bytes);
-    }
-    if (rsp.statusCode != 200) {
-      if (traceLoading) {
-        _log("Got status ${rsp.statusCode} fetching '$resource'.");
-      }
-      return false;
-    }
-    var data = builder.takeBytes();
-    if (traceLoading) {
-      _log("Loaded packages file from '$resource':\n"
-          "${new String.fromCharCodes(data)}");
-    }
-    _parsePackagesFile(sp, traceLoading, resource, data);
-  } catch (e, s) {
-    if (traceLoading) {
-      _log("Error loading packages file from '$resource': $e\n$s");
-    }
-    sp.send("Uncaught error ($e) loading packages file from '$resource'.");
-  }
-  return false;
-}
-
-_loadPackagesData(sp, traceLoading, resource) {
-  try {
-    var data = resource.data;
-    var mime = data.mimeType;
-    if (mime != "text/plain") {
-      throw "MIME-type must be text/plain: $mime given.";
-    }
-    var charset = data.charset;
-    if ((charset != "utf-8") && (charset != "US-ASCII")) {
-      // The C++ portion of the embedder assumes UTF-8.
-      throw "Only utf-8 or US-ASCII encodings are supported: $charset given.";
-    }
-    _parsePackagesFile(sp, traceLoading, resource, data.contentAsBytes());
-  } catch (e) {
-    sp.send("Uncaught error ($e) loading packages data.");
-  }
-}
-
-// This code used to exist in a second isolate and so it uses a SendPort to
-// report it's return value. This could be refactored so that it returns it's
-// value and the caller could wait on the future rather than a message on
-// SendPort.
-_handlePackagesRequest(
-    SendPort sp, bool traceLoading, int tag, Uri resource) async {
-  try {
-    if (tag == -1) {
-      if (resource.scheme == '' || resource.scheme == 'file') {
-        _findPackagesFile(sp, traceLoading, resource);
-      } else if ((resource.scheme == 'http') || (resource.scheme == 'https')) {
-        // Try to load the .packages file next to the resource.
-        var packagesUri = resource.resolve(".packages");
-        var exists = await _loadHttpPackagesFile(sp, traceLoading, packagesUri);
-        if (!exists) {
-          // Loading of the .packages file failed for http/https based scripts
-          sp.send([null]);
-        }
-      } else {
-        sp.send("Unsupported scheme used to locate .packages file: "
-            "'$resource'.");
-      }
-    } else if (tag == -2) {
-      if (traceLoading) {
-        _log("Handling load of packages map: '$resource'.");
-      }
-      if (resource.scheme == '' || resource.scheme == 'file') {
-        var exists = await new File.fromUri(resource).exists();
-        if (exists) {
-          _loadPackagesFile(sp, traceLoading, resource);
-        } else {
-          sp.send("Packages file '$resource' not found.");
-        }
-      } else if ((resource.scheme == 'http') || (resource.scheme == 'https')) {
-        var exists = await _loadHttpPackagesFile(sp, traceLoading, resource);
-        if (!exists) {
-          sp.send("Packages file '$resource' not found.");
-        }
-      } else if (resource.scheme == 'data') {
-        _loadPackagesData(sp, traceLoading, resource);
-      } else {
-        sp.send("Unknown scheme (${resource.scheme}) for package file at "
-            "'$resource'.");
-      }
-    } else {
-      sp.send("Unknown packages request tag: $tag for '$resource'.");
-    }
-  } catch (e, s) {
-    if (traceLoading) {
-      _log("Error handling packages request: $e\n$s");
-    }
-    sp.send("Uncaught error ($e) handling packages request.");
-  }
-}
-
-// Shutdown all active loaders by sending an error message.
-void shutdownLoaders() {
-  String message = 'Service shutdown';
-  if (_httpClient != null) {
-    _httpClient.close(force: true);
-    _httpClient = null;
-  }
-  isolateEmbedderData.values.toList().forEach((ied) {
-    IsolateLoaderState ils = ied;
-    ils.cleanup();
-    assert(ils.sp != null);
-    _sendResourceResponse(ils.sp, 1, null, null, null, message);
-  });
-}
-
-// See Dart_LibraryTag in dart_api.h
-const _Dart_kCanonicalizeUrl = 0; // Canonicalize the URL.
-
-// Extra requests. Keep these in sync between loader.dart and builtin.dart.
-const _Dart_kInitLoader = 4; // Initialize the loader.
-const _Dart_kGetPackageConfigUri = 7; // Uri of the .packages file.
-const _Dart_kResolvePackageUri = 8; // Resolve a package: uri.
-
-// Extra requests. Keep these in sync between loader.dart and loader.cc.
-const _Dart_kImportExtension = 9; // Import a dart-ext: file.
-
-// External entry point for loader requests.
-_processLoadRequest(request) {
-  assert(request is List);
-  assert(request.length > 4);
-
-  // Should we trace loading?
-  bool traceLoading = request[0];
-
-  // This is the sending isolate's Dart_GetMainPortId().
-  int isolateId = request[1];
-
-  // The tag describing the operation.
-  int tag = request[2];
-
-  // The send port to send the response on.
-  SendPort sp = request[3];
-
-  // Grab the loader state for the requesting isolate.
-  IsolateLoaderState loaderState = isolateEmbedderData[isolateId];
-
-  // We are either about to initialize the loader, or, we already have.
-  assert((tag == _Dart_kInitLoader) || (loaderState != null));
-
-  // Handle the request specified in the tag.
-  switch (tag) {
-    case _Dart_kInitLoader:
-      {
-        String packageRoot = request[4];
-        String packagesFile = request[5];
-        String workingDirectory = request[6];
-        String rootScript = request[7];
-        bool isReloading = request[8];
-        if (loaderState == null) {
-          loaderState = new IsolateLoaderState(isolateId);
-          isolateEmbedderData[isolateId] = loaderState;
-          loaderState.init(
-              packageRoot, packagesFile, workingDirectory, rootScript);
-        } else if (isReloading) {
-          loaderState.updatePackageMap(packagesFile);
-        }
-        loaderState.sp = sp;
-        assert(isolateEmbedderData[isolateId] == loaderState);
-      }
-      break;
-    case _Dart_kGetPackageConfigUri:
-      loaderState._triggerPackageResolution(() {
-        // Respond with the packages config (if any) after package resolution.
-        sp.send(loaderState._packageConfig);
-      });
-      break;
-    case _Dart_kResolvePackageUri:
-      Uri uri = Uri.parse(request[4]);
-      loaderState._triggerPackageResolution(() {
-        // Respond with the resolved package uri after package resolution.
-        Uri resolvedUri;
-        try {
-          resolvedUri = loaderState._resolvePackageUri(uri);
-        } catch (e, s) {
-          if (traceLoading) {
-            _log("Exception ($e) when resolving package URI: $uri");
-          }
-          resolvedUri = null;
-        }
-        sp.send(resolvedUri);
-      });
-      break;
-    case _Dart_kImportExtension:
-      Uri uri = Uri.parse(request[4]);
-      String libraryUri = request[5];
-      // Strip any filename off of the libraryUri's path.
-      int index = libraryUri.lastIndexOf('/');
-      var path;
-      if (index == -1) {
-        path = './';
-      } else {
-        path = libraryUri.substring(0, index + 1);
-      }
-      var pathUri = Uri.parse(path);
-      switch (pathUri.scheme) {
-        case '':
-        case 'file':
-          _sendExtensionImportResponse(
-              sp, uri, libraryUri, pathUri.toFilePath());
-          break;
-        case 'data':
-        case 'http':
-        case 'https':
-          _sendExtensionImportResponse(sp, uri, libraryUri, pathUri.toString());
-          break;
-        case 'package':
-          // Start package resolution.
-          loaderState._triggerPackageResolution(() {
-            // Attempt to find the fully resolved uri of [path].
-            Uri resolvedUri;
-            try {
-              resolvedUri = loaderState._resolvePackageUri(pathUri);
-            } catch (e, s) {
-              if (traceLoading) {
-                _log("Exception ($e) when resolving package URI: $uri");
-              }
-              resolvedUri = null;
-            }
-            _sendExtensionImportResponse(
-                sp, uri, libraryUri, resolvedUri.toString());
-          });
-          break;
-        default:
-          if (traceLoading) {
-            _log('Unknown scheme (${pathUri.scheme}) in $pathUri.');
-          }
-          _sendExtensionImportResponse(sp, uri, libraryUri, null);
-          break;
-      }
-      break;
-    default:
-      _log('Unknown loader request tag=$tag from $isolateId');
-  }
-}
diff --git a/runtime/bin/vmservice/vmservice_io.dart b/runtime/bin/vmservice/vmservice_io.dart
index 4ed2f63b340..46fb27eebd8 100644
--- a/runtime/bin/vmservice/vmservice_io.dart
+++ b/runtime/bin/vmservice/vmservice_io.dart
@@ -14,7 +14,6 @@ import 'dart:isolate';
 import 'dart:typed_data';
 import 'dart:_vmservice';
 
-part 'loader.dart';
 part 'server.dart';
 
 // The TCP ip/port that the HTTP server listens on.
@@ -58,7 +57,6 @@ _lazyServerBoot() {
 }
 
 Future cleanupCallback() async {
-  shutdownLoaders();
   // Cancel the sigquit subscription.
   if (_signalSubscription != null) {
     await _signalSubscription.cancel();
@@ -264,11 +262,9 @@ main() {
     // scheduled microtasks.
     Timer.run(() {});
   }
-  scriptLoadPort.handler = _processLoadRequest;
   // Register signal handler after a small delay to avoid stalling main
   // isolate startup.
   _registerSignalHandlerTimer = new Timer(shortDelay, _registerSignalHandler);
-  return scriptLoadPort;
 }
 
 _shutdown() native "VMServiceIO_Shutdown";
diff --git a/runtime/bin/vmservice/vmservice_sources.gni b/runtime/bin/vmservice/vmservice_sources.gni
index 4c5d0c6d112..d326c2aec2e 100644
--- a/runtime/bin/vmservice/vmservice_sources.gni
+++ b/runtime/bin/vmservice/vmservice_sources.gni
@@ -5,7 +5,6 @@
 # This file contains all Dart sources for the dart:io implementation of
 # the VM Service server.
 vmservice_sources = [
-  "loader.dart",
   "server.dart",
   "vmservice_io.dart",
 ]
diff --git a/runtime/include/dart_api.h b/runtime/include/dart_api.h
index cfc6cd975dc..aff0896aa25 100644
--- a/runtime/include/dart_api.h
+++ b/runtime/include/dart_api.h
@@ -3261,14 +3261,6 @@ DART_EXPORT void Dart_SetDartLibrarySourcesKernel(
  */
 DART_EXPORT bool Dart_IsServiceIsolate(Dart_Isolate isolate);
 
-/**
- * Returns the port that script load requests should be sent on.
- *
- * \return Returns the port for load requests or ILLEGAL_PORT if the service
- * isolate failed to startup or does not support load requests.
- */
-DART_EXPORT Dart_Port Dart_ServiceWaitForLoadPort();
-
 /**
  * Writes the CPU profile to the timeline as a series of 'instant' events.
  *
diff --git a/runtime/vm/dart_api_impl.cc b/runtime/vm/dart_api_impl.cc
index b578116853b..9df042e182a 100644
--- a/runtime/vm/dart_api_impl.cc
+++ b/runtime/vm/dart_api_impl.cc
@@ -5732,10 +5732,6 @@ DART_EXPORT bool Dart_IsServiceIsolate(Dart_Isolate isolate) {
   return ServiceIsolate::IsServiceIsolate(iso);
 }
 
-DART_EXPORT Dart_Port Dart_ServiceWaitForLoadPort() {
-  return ServiceIsolate::WaitForLoadPort();
-}
-
 DART_EXPORT int64_t Dart_TimelineGetMicros() {
   return OS::GetCurrentMonotonicMicros();
 }
diff --git a/runtime/vm/service_isolate.cc b/runtime/vm/service_isolate.cc
index 2ddd7deb094..211b5948e57 100644
--- a/runtime/vm/service_isolate.cc
+++ b/runtime/vm/service_isolate.cc
@@ -78,7 +78,6 @@ Monitor* ServiceIsolate::monitor_ = new Monitor();
 ServiceIsolate::State ServiceIsolate::state_ = ServiceIsolate::kStopped;
 Isolate* ServiceIsolate::isolate_ = NULL;
 Dart_Port ServiceIsolate::port_ = ILLEGAL_PORT;
-Dart_Port ServiceIsolate::load_port_ = ILLEGAL_PORT;
 Dart_Port ServiceIsolate::origin_ = ILLEGAL_PORT;
 char* ServiceIsolate::server_address_ = NULL;
 char* ServiceIsolate::startup_failure_reason_ = nullptr;
@@ -142,22 +141,11 @@ Dart_Port ServiceIsolate::Port() {
   return port_;
 }
 
-Dart_Port ServiceIsolate::WaitForLoadPort() {
-  VMTagScope tagScope(Thread::Current(), VMTag::kLoadWaitTagId);
-  return WaitForLoadPortInternal();
-}
-
-Dart_Port ServiceIsolate::WaitForLoadPortInternal() {
+void ServiceIsolate::WaitForServiceIsolateStartup() {
   MonitorLocker ml(monitor_);
-  while (state_ == kStarting && (load_port_ == ILLEGAL_PORT)) {
+  while (state_ == kStarting) {
     ml.Wait();
   }
-  return load_port_;
-}
-
-Dart_Port ServiceIsolate::LoadPort() {
-  MonitorLocker ml(monitor_);
-  return load_port_;
 }
 
 bool ServiceIsolate::SendServiceRpc(uint8_t* request_json,
@@ -190,8 +178,7 @@ bool ServiceIsolate::SendServiceRpc(uint8_t* request_json,
   request.type = Dart_CObject_kArray;
   request.value.as_array.values = request_array;
   request.value.as_array.length = ARRAY_SIZE(request_array);
-
-  ServiceIsolate::WaitForLoadPortInternal();
+  ServiceIsolate::WaitForServiceIsolateStartup();
   Dart_Port service_port = ServiceIsolate::Port();
 
   const bool success = Dart_PostCObject(service_port, &request);
@@ -303,11 +290,6 @@ void ServiceIsolate::SetServiceIsolate(Isolate* isolate) {
   }
 }
 
-void ServiceIsolate::SetLoadPort(Dart_Port port) {
-  MonitorLocker ml(monitor_);
-  load_port_ = port;
-}
-
 void ServiceIsolate::MaybeMakeServiceIsolate(Isolate* I) {
   Thread* T = Thread::Current();
   ASSERT(I == T->isolate());
@@ -452,7 +434,7 @@ class RunServiceTask : public ThreadPool::Task {
     ASSERT(I == T->isolate());
     StackZone zone(T);
     HANDLESCOPE(T);
-    // Invoke main which will return the loadScriptPort.
+    // Invoke main which will set up the service port.
     const Library& root_library =
         Library::Handle(Z, I->object_store()->root_library());
     if (root_library.IsNull()) {
@@ -479,7 +461,6 @@ class RunServiceTask : public ThreadPool::Task {
     ASSERT(!entry.IsNull());
     const Object& result = Object::Handle(
         Z, DartEntry::InvokeFunction(entry, Object::empty_array()));
-    ASSERT(!result.IsNull());
     if (result.IsError()) {
       // Service isolate did not initialize properly.
       if (FLAG_trace_service) {
@@ -493,9 +474,6 @@ class RunServiceTask : public ThreadPool::Task {
       }
       return false;
     }
-    ASSERT(result.IsReceivePort());
-    const ReceivePort& rp = ReceivePort::Cast(result);
-    ServiceIsolate::SetLoadPort(rp.Id());
     return false;
   }
 };
diff --git a/runtime/vm/service_isolate.h b/runtime/vm/service_isolate.h
index a3c1fdfd11c..8940f6ac010 100644
--- a/runtime/vm/service_isolate.h
+++ b/runtime/vm/service_isolate.h
@@ -26,9 +26,7 @@ class ServiceIsolate : public AllStatic {
   static bool IsServiceIsolate(const Isolate* isolate);
   static bool IsServiceIsolateDescendant(const Isolate* isolate);
   static Dart_Port Port();
-
-  static Dart_Port WaitForLoadPort();
-  static Dart_Port LoadPort();
+  static void WaitForServiceIsolateStartup();
 
   // Returns `true` if the request was sucessfully sent.  If it was, the
   // [reply_port] will receive a Dart_TypedData_kUint8 response json.
@@ -62,13 +60,9 @@ class ServiceIsolate : public AllStatic {
  private:
   static void KillServiceIsolate();
 
-  // Does not need a current thread.
-  static Dart_Port WaitForLoadPortInternal();
-
  protected:
   static void SetServicePort(Dart_Port port);
   static void SetServiceIsolate(Isolate* isolate);
-  static void SetLoadPort(Dart_Port port);
   static void FinishedExiting();
   static void FinishedInitializing();
   static void InitializingFailed(char* error);
@@ -88,7 +82,6 @@ class ServiceIsolate : public AllStatic {
   static State state_;
   static Isolate* isolate_;
   static Dart_Port port_;
-  static Dart_Port load_port_;
   static Dart_Port origin_;
   static char* server_address_;
 
diff --git a/sdk/lib/_internal/vm/bin/builtin.dart b/sdk/lib/_internal/vm/bin/builtin.dart
index 6977c89af53..b79755ef7ec 100644
--- a/sdk/lib/_internal/vm/bin/builtin.dart
+++ b/sdk/lib/_internal/vm/bin/builtin.dart
@@ -10,6 +10,7 @@ library builtin;
 import 'dart:async';
 import 'dart:collection' hide LinkedList, LinkedListEntry;
 import 'dart:_internal' hide Symbol;
+import 'dart:io';
 import 'dart:isolate';
 import 'dart:typed_data';
 
@@ -33,48 +34,30 @@ void _print(arg) {
 @pragma("vm:entry-point")
 _getPrintClosure() => _print;
 
-// Asynchronous loading of resources.
-// The embedder forwards loading requests to the service isolate.
-
-// A port for communicating with the service isolate for I/O.
-@pragma("vm:entry-point")
-SendPort _loadPort;
-
-// The isolateId used to communicate with the service isolate for I/O.
-@pragma("vm:entry-point")
-int _isolateId;
-
-// Requests made to the service isolate over the load port.
-
-// Extra requests. Keep these in sync between loader.dart and builtin.dart.
-const _Dart_kGetPackageConfigUri = 7; // Uri of the .packages file.
-const _Dart_kResolvePackageUri = 8; // Resolve a package: uri.
-
-// Make a request to the loader. Future will complete with result which is
-// either a Uri or a List<int>.
-Future<T> _makeLoaderRequest<T>(int tag, String uri) {
-  assert(_isolateId != null);
-  if (_loadPort == null) {
-    throw new UnsupportedError("Service isolate is not available.");
-  }
-  Completer completer = new Completer<T>();
-  RawReceivePort port = new RawReceivePort();
-  port.handler = (msg) {
-    // Close the port.
-    port.close();
-    completer.complete(msg);
-  };
-  _loadPort.send([_traceLoading, _isolateId, tag, port.sendPort, uri]);
-  return completer.future;
-}
-
 // The current working directory when the embedder was launched.
 Uri _workingDirectory;
+
 // The URI that the root script was loaded from. Remembered so that
 // package imports can be resolved relative to it. The root script is the basis
 // for the root library in the VM.
 Uri _rootScript;
 
+// packagesConfig specified for the isolate.
+Uri _packagesConfigUri;
+
+// Packages are either resolved looking up in a map or resolved from within a
+// package root.
+bool get _packagesReady => (_packageMap != null) || (_packageError != null);
+
+// Error string set if there was an error resolving package configuration.
+// For example not finding a .packages file or packages/ directory, malformed
+// .packages file or any other related error.
+String _packageError = null;
+
+// The map describing how certain package names are mapped to Uris.
+Uri _packageConfig = null;
+Map<String, Uri> _packageMap = null;
+
 // Special handling for Windows paths so that they are compatible with URI
 // handling.
 // Embedder sets this to true if we are running on Windows.
@@ -111,29 +94,473 @@ _sanitizeWindowsPath(path) {
   return fixedPath;
 }
 
-_trimWindowsPath(path) {
-  // Convert /X:/ to X:/.
-  if (_isWindows == false) {
-    // Do nothing when not running Windows.
-    return path;
+_setPackagesConfig(String packagesParam) {
+  var packagesName = _sanitizeWindowsPath(packagesParam);
+  var packagesUri = Uri.parse(packagesName);
+  if (packagesUri.scheme == '') {
+    // Script does not have a scheme, assume that it is a path,
+    // resolve it against the working directory.
+    packagesUri = _workingDirectory.resolveUri(packagesUri);
   }
-  if (!path.startsWith('/') || (path.length < 3)) {
-    return path;
-  }
-  // Match '/?:'.
-  if ((path[0] == '/') && (path[2] == ':')) {
-    // Remove leading '/'.
-    return path.substring(1);
-  }
-  return path;
+  _packagesConfigUri = packagesUri;
 }
 
-// Ensure we have a trailing slash character.
-_enforceTrailingSlash(uri) {
-  if (!uri.endsWith('/')) {
-    return '$uri/';
+// Given a uri with a 'package' scheme, return a Uri that is prefixed with
+// the package root or resolved relative to the package configuration.
+Uri _resolvePackageUri(Uri uri) {
+  assert(uri.scheme == "package");
+  assert(_packagesReady);
+
+  if (uri.host.isNotEmpty) {
+    var path = '${uri.host}${uri.path}';
+    var right = 'package:$path';
+    var wrong = 'package://$path';
+
+    throw "URIs using the 'package:' scheme should look like "
+        "'$right', not '$wrong'.";
+  }
+
+  var packageNameEnd = uri.path.indexOf('/');
+  if (packageNameEnd == 0) {
+    // Package URIs must have a non-empty package name (not start with "/").
+    throw "URIS using the 'package:' scheme should look like "
+        "'package:packageName${uri.path}', not 'package:${uri.path}'";
+  }
+  if (_traceLoading) {
+    _log('Resolving package with uri path: ${uri.path}');
+  }
+  var resolvedUri;
+  if (_packageError != null) {
+    if (_traceLoading) {
+      _log("Resolving package with pending resolution error: $_packageError");
+    }
+    throw _packageError;
+  } else {
+    if (packageNameEnd < 0) {
+      // Package URIs must have a path after the package name, even if it's
+      // just "/".
+      throw "URIS using the 'package:' scheme should look like "
+          "'package:${uri.path}/', not 'package:${uri.path}'";
+    }
+    var packageName = uri.path.substring(0, packageNameEnd);
+    var mapping = _packageMap[packageName];
+    if (_traceLoading) {
+      _log("Mapped '$packageName' package to '$mapping'");
+    }
+    if (mapping == null) {
+      throw "No mapping for '$packageName' package when resolving '$uri'.";
+    }
+    var path;
+    assert(uri.path.length > packageName.length);
+    path = uri.path.substring(packageName.length + 1);
+    if (_traceLoading) {
+      _log("Path to be resolved in package: $path");
+    }
+    resolvedUri = mapping.resolve(path);
+  }
+  if (_traceLoading) {
+    _log("Resolved '$uri' to '$resolvedUri'.");
+  }
+  return resolvedUri;
+}
+
+void _requestPackagesMap(Uri packageConfig) {
+  dynamic msg = null;
+  if (packageConfig != null) {
+    // Explicitly specified .packages path.
+    msg = _handlePackagesRequest(_traceLoading, -2, packageConfig);
+  } else {
+    // Search for .packages starting at the root script.
+    msg = _handlePackagesRequest(_traceLoading, -1, _rootScript);
+  }
+  if (_traceLoading) {
+    _log("Requested packages map for '$_rootScript'.");
+  }
+  if (msg is String) {
+    if (_traceLoading) {
+      _log("Got failure response on package port: '$msg'");
+    }
+    // Remember the error message.
+    _packageError = msg;
+  } else if (msg is List) {
+    // First entry contains the location of the loaded .packages file.
+    assert((msg.length % 2) == 0);
+    assert(msg.length >= 2);
+    assert(msg[1] == null);
+    _packageConfig = Uri.parse(msg[0]);
+    _packageMap = new Map<String, Uri>();
+    for (var i = 2; i < msg.length; i += 2) {
+      // TODO(iposva): Complain about duplicate entries.
+      _packageMap[msg[i]] = Uri.parse(msg[i + 1]);
+    }
+    if (_traceLoading) {
+      _log("Setup package map: $_packageMap");
+    }
+  } else {
+    _packageError = "Bad type of packages reply: ${msg.runtimeType}";
+    if (_traceLoading) {
+      _log(_packageError);
+    }
+  }
+}
+
+// Handling of packages requests. Finding and parsing of .packages file or
+// packages/ directories.
+const _LF = 0x0A;
+const _CR = 0x0D;
+const _SPACE = 0x20;
+const _HASH = 0x23;
+const _DOT = 0x2E;
+const _COLON = 0x3A;
+const _DEL = 0x7F;
+
+const _invalidPackageNameChars = const [
+  true, //  space
+  false, // !
+  true, //  "
+  true, //  #
+  false, // $
+  true, //  %
+  false, // &
+  false, // '
+  false, // (
+  false, // )
+  false, // *
+  false, // +
+  false, // ,
+  false, // -
+  false, // .
+  true, //  /
+  false, // 0
+  false, // 1
+  false, // 2
+  false, // 3
+  false, // 4
+  false, // 5
+  false, // 6
+  false, // 7
+  false, // 8
+  false, // 9
+  true, //  :
+  false, // ;
+  true, //  <
+  false, // =
+  true, //  >
+  true, //  ?
+  false, // @
+  false, // A
+  false, // B
+  false, // C
+  false, // D
+  false, // E
+  false, // F
+  false, // G
+  false, // H
+  false, // I
+  false, // J
+  false, // K
+  false, // L
+  false, // M
+  false, // N
+  false, // O
+  false, // P
+  false, // Q
+  false, // R
+  false, // S
+  false, // T
+  false, // U
+  false, // V
+  false, // W
+  false, // X
+  false, // Y
+  false, // Z
+  true, //  [
+  true, //  \
+  true, //  ]
+  true, //  ^
+  false, // _
+  true, //  `
+  false, // a
+  false, // b
+  false, // c
+  false, // d
+  false, // e
+  false, // f
+  false, // g
+  false, // h
+  false, // i
+  false, // j
+  false, // k
+  false, // l
+  false, // m
+  false, // n
+  false, // o
+  false, // p
+  false, // q
+  false, // r
+  false, // s
+  false, // t
+  false, // u
+  false, // v
+  false, // w
+  false, // x
+  false, // y
+  false, // z
+  true, //  {
+  true, //  |
+  true, //  }
+  false, // ~
+  true, //  DEL
+];
+
+_parsePackagesFile(bool traceLoading, Uri packagesFile, List<int> data) {
+  // The first entry contains the location of the identified .packages file
+  // instead of a mapping.
+  var result = [packagesFile.toString(), null];
+  var index = 0;
+  var len = data.length;
+  while (index < len) {
+    var start = index;
+    var char = data[index];
+    if ((char == _CR) || (char == _LF)) {
+      // Skipping empty lines.
+      index++;
+      continue;
+    }
+
+    // Identify split within the line and end of the line.
+    var separator = -1;
+    var end = len;
+    // Verifying validity of package name while scanning the line.
+    var nonDot = false;
+    var invalidPackageName = false;
+
+    // Scan to the end of the line or data.
+    while (index < len) {
+      char = data[index++];
+      // If we have not reached the separator yet, determine whether we are
+      // scanning legal package name characters.
+      if (separator == -1) {
+        if ((char == _COLON)) {
+          // The first colon on a line is the separator between package name and
+          // related URI.
+          separator = index - 1;
+        } else {
+          // Still scanning the package name part. Check for the validity of
+          // the characters.
+          nonDot = nonDot || (char != _DOT);
+          invalidPackageName = invalidPackageName ||
+              (char < _SPACE) ||
+              (char > _DEL) ||
+              _invalidPackageNameChars[char - _SPACE];
+        }
+      }
+      // Identify end of line.
+      if ((char == _CR) || (char == _LF)) {
+        end = index - 1;
+        break;
+      }
+    }
+
+    // No further handling needed for comment lines.
+    if (data[start] == _HASH) {
+      if (traceLoading) {
+        _log("Skipping comment in $packagesFile:\n"
+            "${new String.fromCharCodes(data, start, end)}");
+      }
+      continue;
+    }
+
+    // Check for a badly formatted line, starting with a ':'.
+    if (separator == start) {
+      var line = new String.fromCharCodes(data, start, end);
+      if (traceLoading) {
+        _log("Line starts with ':' in $packagesFile:\n"
+            "$line");
+      }
+      return "Missing package name in $packagesFile:\n"
+          "$line";
+    }
+
+    // Ensure there is a separator on the line.
+    if (separator == -1) {
+      var line = new String.fromCharCodes(data, start, end);
+      if (traceLoading) {
+        _log("Line has no ':' in $packagesFile:\n"
+            "$line");
+      }
+      return "Missing ':' separator in $packagesFile:\n"
+          "$line";
+    }
+
+    var packageName = new String.fromCharCodes(data, start, separator);
+
+    // Check for valid package name.
+    if (invalidPackageName || !nonDot) {
+      var line = new String.fromCharCodes(data, start, end);
+      if (traceLoading) {
+        _log("Invalid package name $packageName in $packagesFile");
+      }
+      return "Invalid package name '$packageName' in $packagesFile:\n"
+          "$line";
+    }
+
+    if (traceLoading) {
+      _log("packageName: $packageName");
+    }
+    var packageUri = new String.fromCharCodes(data, separator + 1, end);
+    if (traceLoading) {
+      _log("original packageUri: $packageUri");
+    }
+    // Ensure the package uri ends with a /.
+    if (!packageUri.endsWith("/")) {
+      packageUri = "$packageUri/";
+    }
+    packageUri = packagesFile.resolve(packageUri).toString();
+    if (traceLoading) {
+      _log("mapping: $packageName -> $packageUri");
+    }
+    result.add(packageName);
+    result.add(packageUri);
+  }
+
+  if (traceLoading) {
+    _log("Parsed packages file at $packagesFile. Sending:\n$result");
+  }
+  return result;
+}
+
+_loadPackagesFile(bool traceLoading, Uri packagesFile) {
+  try {
+    var data = new File.fromUri(packagesFile).readAsBytesSync();
+    if (traceLoading) {
+      _log("Loaded packages file from $packagesFile:\n"
+          "${new String.fromCharCodes(data)}");
+    }
+    return _parsePackagesFile(traceLoading, packagesFile, data);
+  } catch (e, s) {
+    if (traceLoading) {
+      _log("Error loading packages: $e\n$s");
+    }
+    return "Uncaught error ($e) loading packages file.";
+  }
+}
+
+_findPackagesFile(bool traceLoading, Uri base) {
+  try {
+    // Walk up the directory hierarchy to check for the existence of
+    // .packages files in parent directories and for the existence of a
+    // packages/ directory on the first iteration.
+    var dir = new File.fromUri(base).parent;
+    var prev = null;
+    // Keep searching until we reach the root.
+    while ((prev == null) || (prev.path != dir.path)) {
+      // Check for the existence of a .packages file and if it exists try to
+      // load and parse it.
+      var dirUri = dir.uri;
+      var packagesFile = dirUri.resolve(".packages");
+      if (traceLoading) {
+        _log("Checking for $packagesFile file.");
+      }
+      var exists = new File.fromUri(packagesFile).existsSync();
+      if (traceLoading) {
+        _log("$packagesFile exists: $exists");
+      }
+      if (exists) {
+        return _loadPackagesFile(traceLoading, packagesFile);
+      }
+      // Move up one level.
+      prev = dir;
+      dir = dir.parent;
+    }
+
+    // No .packages file was found.
+    if (traceLoading) {
+      _log("Could not resolve a package location from $base");
+    }
+    return "Could not resolve a package location for base at $base";
+  } catch (e, s) {
+    if (traceLoading) {
+      _log("Error loading packages: $e\n$s");
+    }
+    return "Uncaught error ($e) loading packages file.";
+  }
+}
+
+_loadPackagesData(traceLoading, resource) {
+  try {
+    var data = resource.data;
+    var mime = data.mimeType;
+    if (mime != "text/plain") {
+      throw "MIME-type must be text/plain: $mime given.";
+    }
+    var charset = data.charset;
+    if ((charset != "utf-8") && (charset != "US-ASCII")) {
+      // The C++ portion of the embedder assumes UTF-8.
+      throw "Only utf-8 or US-ASCII encodings are supported: $charset given.";
+    }
+    return _parsePackagesFile(traceLoading, resource, data.contentAsBytes());
+  } catch (e) {
+    return "Uncaught error ($e) loading packages data.";
+  }
+}
+
+_handlePackagesRequest(bool traceLoading, int tag, Uri resource) {
+  try {
+    if (tag == -1) {
+      if (resource.scheme == '' || resource.scheme == 'file') {
+        return _findPackagesFile(traceLoading, resource);
+      } else {
+        return "Unsupported scheme used to locate .packages file:'$resource'.";
+      }
+    } else if (tag == -2) {
+      if (traceLoading) {
+        _log("Handling load of packages map: '$resource'.");
+      }
+      if (resource.scheme == '' || resource.scheme == 'file') {
+        var exists = new File.fromUri(resource).existsSync();
+        if (exists) {
+          return _loadPackagesFile(traceLoading, resource);
+        } else {
+          return "Packages file '$resource' not found.";
+        }
+      } else if (resource.scheme == 'data') {
+        return _loadPackagesData(traceLoading, resource);
+      } else {
+        return "Unknown scheme (${resource.scheme}) for package file at "
+            "'$resource'.";
+      }
+    } else {
+      return "Unknown packages request tag: $tag for '$resource'.";
+    }
+  } catch (e, s) {
+    if (traceLoading) {
+      _log("Error handling packages request: $e\n$s");
+    }
+    return "Uncaught error ($e) handling packages request.";
+  }
+}
+
+// Embedder Entrypoint:
+// The embedder calls this method to initial the package resolution state.
+@pragma("vm:entry-point")
+void _Init(String packagesConfig, String workingDirectory, String rootScript) {
+  // Register callbacks and hooks with the rest of core libraries.
+  _setupHooks();
+
+  // _workingDirectory must be set first.
+  _workingDirectory = new Uri.directory(workingDirectory);
+
+  // setup _rootScript.
+  if (rootScript != null) {
+    _rootScript = Uri.parse(rootScript);
+  }
+
+  // If the --packages flag was passed, setup _packagesConfig.
+  if (packagesConfig != null) {
+    _packageMap = null;
+    _setPackagesConfig(packagesConfig);
   }
-  return uri;
 }
 
 // Embedder Entrypoint:
@@ -224,11 +651,14 @@ Future<Uri> _getPackageConfigFuture() {
   if (_traceLoading) {
     _log("Request for package config from user code.");
   }
-  assert(_loadPort != null);
-  return _makeLoaderRequest<Uri>(_Dart_kGetPackageConfigUri, null);
+  if (!_packagesReady) {
+    _requestPackagesMap(_packagesConfigUri);
+  }
+  // Respond with the packages config (if any) after package resolution.
+  return Future.value(_packageConfig);
 }
 
-Future<Uri> _resolvePackageUriFuture(Uri packageUri) async {
+Future<Uri> _resolvePackageUriFuture(Uri packageUri) {
   if (_traceLoading) {
     _log("Request for package Uri resolution from user code: $packageUri");
   }
@@ -237,18 +667,22 @@ Future<Uri> _resolvePackageUriFuture(Uri packageUri) async {
       _log("Non-package Uri, returning unmodified: $packageUri");
     }
     // Return the incoming parameter if not passed a package: URI.
-    return packageUri;
+    return Future.value(packageUri);
   }
-  var result = await _makeLoaderRequest<Uri>(
-      _Dart_kResolvePackageUri, packageUri.toString());
-  if (result is! Uri) {
+  if (!_packagesReady) {
+    _requestPackagesMap(_packagesConfigUri);
+  }
+  Uri resolvedUri;
+  try {
+    resolvedUri = _resolvePackageUri(packageUri);
+  } catch (e, s) {
     if (_traceLoading) {
       _log("Exception when resolving package URI: $packageUri");
     }
-    result = null;
+    resolvedUri = null;
   }
   if (_traceLoading) {
-    _log("Resolved '$packageUri' to '$result'");
+    _log("Resolved '$packageUri' to '$resolvedUri'");
   }
-  return result;
+  return Future.value(resolvedUri);
 }
diff --git a/sdk_nnbd/lib/_internal/vm/bin/builtin.dart b/sdk_nnbd/lib/_internal/vm/bin/builtin.dart
index a569688197d..f202b3f6187 100644
--- a/sdk_nnbd/lib/_internal/vm/bin/builtin.dart
+++ b/sdk_nnbd/lib/_internal/vm/bin/builtin.dart
@@ -10,6 +10,7 @@ library builtin;
 import 'dart:async';
 import 'dart:collection' hide LinkedList, LinkedListEntry;
 import 'dart:_internal' hide Symbol;
+import 'dart:io';
 import 'dart:isolate';
 import 'dart:typed_data';
 
@@ -33,48 +34,30 @@ void _print(arg) {
 @pragma("vm:entry-point")
 _getPrintClosure() => _print;
 
-// Asynchronous loading of resources.
-// The embedder forwards loading requests to the service isolate.
-
-// A port for communicating with the service isolate for I/O.
-@pragma("vm:entry-point")
-SendPort _loadPort;
-
-// The isolateId used to communicate with the service isolate for I/O.
-@pragma("vm:entry-point")
-int _isolateId;
-
-// Requests made to the service isolate over the load port.
-
-// Extra requests. Keep these in sync between loader.dart and builtin.dart.
-const _Dart_kGetPackageConfigUri = 7; // Uri of the .packages file.
-const _Dart_kResolvePackageUri = 8; // Resolve a package: uri.
-
-// Make a request to the loader. Future will complete with result which is
-// either a Uri or a List<int>.
-Future<T> _makeLoaderRequest<T>(int tag, String uri) {
-  assert(_isolateId != null);
-  if (_loadPort == null) {
-    throw new UnsupportedError("Service isolate is not available.");
-  }
-  Completer completer = new Completer<T>();
-  RawReceivePort port = new RawReceivePort();
-  port.handler = (msg) {
-    // Close the port.
-    port.close();
-    completer.complete(msg);
-  };
-  _loadPort.send([_traceLoading, _isolateId, tag, port.sendPort, uri]);
-  return completer.future;
-}
-
 // The current working directory when the embedder was launched.
 Uri _workingDirectory;
+
 // The URI that the root script was loaded from. Remembered so that
 // package imports can be resolved relative to it. The root script is the basis
 // for the root library in the VM.
 Uri _rootScript;
 
+// packagesConfig specified for the isolate.
+Uri _packagesConfigUri;
+
+// Packages are either resolved looking up in a map or resolved from within a
+// package root.
+bool get _packagesReady => (_packageMap != null) || (_packageError != null);
+
+// Error string set if there was an error resolving package configuration.
+// For example not finding a .packages file or packages/ directory, malformed
+// .packages file or any other related error.
+String _packageError = null;
+
+// The map describing how certain package names are mapped to Uris.
+Uri _packageConfig = null;
+Map<String, Uri> _packageMap = null;
+
 // Special handling for Windows paths so that they are compatible with URI
 // handling.
 // Embedder sets this to true if we are running on Windows.
@@ -111,29 +94,474 @@ _sanitizeWindowsPath(path) {
   return fixedPath;
 }
 
-_trimWindowsPath(path) {
-  // Convert /X:/ to X:/.
-  if (_isWindows == false) {
-    // Do nothing when not running Windows.
-    return path;
+_setPackagesConfig(String packagesParam) {
+  var packagesName = _sanitizeWindowsPath(packagesParam);
+  var packagesUri = Uri.parse(packagesName);
+  if (packagesUri.scheme == '') {
+    // Script does not have a scheme, assume that it is a path,
+    // resolve it against the working directory.
+    packagesUri = _workingDirectory.resolveUri(packagesUri);
   }
-  if (!path.startsWith('/') || (path.length < 3)) {
-    return path;
-  }
-  // Match '/?:'.
-  if ((path[0] == '/') && (path[2] == ':')) {
-    // Remove leading '/'.
-    return path.substring(1);
-  }
-  return path;
+  _packagesConfigUri = packagesUri;
 }
 
-// Ensure we have a trailing slash character.
-_enforceTrailingSlash(uri) {
-  if (!uri.endsWith('/')) {
-    return '$uri/';
+// Given a uri with a 'package' scheme, return a Uri that is prefixed with
+// the package root or resolved relative to the package configuration.
+Uri _resolvePackageUri(Uri uri) {
+  assert(uri.scheme == "package");
+  assert(_packagesReady);
+
+  if (uri.host.isNotEmpty) {
+    var path = '${uri.host}${uri.path}';
+    var right = 'package:$path';
+    var wrong = 'package://$path';
+
+    throw "URIs using the 'package:' scheme should look like "
+        "'$right', not '$wrong'.";
+  }
+
+  var packageNameEnd = uri.path.indexOf('/');
+  if (packageNameEnd == 0) {
+    // Package URIs must have a non-empty package name (not start with "/").
+    throw "URIS using the 'package:' scheme should look like "
+        "'package:packageName${uri.path}', not 'package:${uri.path}'";
+  }
+  if (_traceLoading) {
+    _log('Resolving package with uri path: ${uri.path}');
+  }
+  var resolvedUri;
+  if (_packageError != null) {
+    if (_traceLoading) {
+      _log("Resolving package with pending resolution error: $_packageError");
+    }
+    throw _packageError;
+  } else {
+    if (packageNameEnd < 0) {
+      // Package URIs must have a path after the package name, even if it's
+      // just "/".
+      throw "URIS using the 'package:' scheme should look like "
+          "'package:${uri.path}/', not 'package:${uri.path}'";
+    }
+    var packageName = uri.path.substring(0, packageNameEnd);
+    var mapping = _packageMap[packageName];
+    if (_traceLoading) {
+      _log("Mapped '$packageName' package to '$mapping'");
+    }
+    if (mapping == null) {
+      throw "No mapping for '$packageName' package when resolving '$uri'.";
+    }
+    var path;
+    assert(uri.path.length > packageName.length);
+    path = uri.path.substring(packageName.length + 1);
+    if (_traceLoading) {
+      _log("Path to be resolved in package: $path");
+    }
+    resolvedUri = mapping.resolve(path);
+  }
+  if (_traceLoading) {
+    _log("Resolved '$uri' to '$resolvedUri'.");
+  }
+  return resolvedUri;
+}
+
+void _requestPackagesMap(Uri packageConfig) {
+  var msg = null;
+  if (packageConfig != null) {
+    // Explicitly specified .packages path.
+    msg = _handlePackagesRequest(_traceLoading, -2, packageConfig);
+  } else {
+    // Search for .packages starting at the root script.
+    msg = _handlePackagesRequest(_traceLoading, -1, _rootScript);
+  }
+  if (_traceLoading) {
+    _log("Requested packages map for '$_rootScript'.");
+  }
+  if (msg is String) {
+    if (_traceLoading) {
+      _log("Got failure response on package port: '$msg'");
+    }
+    // Remember the error message.
+    _packageError = msg;
+  } else if (msg is List) {
+    // First entry contains the location of the loaded .packages file.
+    assert((msg.length % 2) == 0);
+    assert(msg.length >= 2);
+    assert(msg[1] == null);
+    _packageConfig = Uri.parse(msg[0]);
+    _packageMap = new Map<String, Uri>();
+    for (var i = 2; i < msg.length; i += 2) {
+      // TODO(iposva): Complain about duplicate entries.
+      _packageMap[msg[i]] = Uri.parse(msg[i + 1]);
+    }
+    if (_traceLoading) {
+      _log("Setup package map: $_packageMap");
+    }
+  } else {
+    _packageError = "Bad type of packages reply: ${msg.runtimeType}";
+    if (_traceLoading) {
+      _log(_packageError);
+    }
+  }
+}
+
+// Handling of packages requests. Finding and parsing of .packages file or
+// packages/ directories.
+const _LF = 0x0A;
+const _CR = 0x0D;
+const _SPACE = 0x20;
+const _HASH = 0x23;
+const _DOT = 0x2E;
+const _COLON = 0x3A;
+const _DEL = 0x7F;
+
+const _invalidPackageNameChars = const [
+  true, //  space
+  false, // !
+  true, //  "
+  true, //  #
+  false, // $
+  true, //  %
+  false, // &
+  false, // '
+  false, // (
+  false, // )
+  false, // *
+  false, // +
+  false, // ,
+  false, // -
+  false, // .
+  true, //  /
+  false, // 0
+  false, // 1
+  false, // 2
+  false, // 3
+  false, // 4
+  false, // 5
+  false, // 6
+  false, // 7
+  false, // 8
+  false, // 9
+  true, //  :
+  false, // ;
+  true, //  <
+  false, // =
+  true, //  >
+  true, //  ?
+  false, // @
+  false, // A
+  false, // B
+  false, // C
+  false, // D
+  false, // E
+  false, // F
+  false, // G
+  false, // H
+  false, // I
+  false, // J
+  false, // K
+  false, // L
+  false, // M
+  false, // N
+  false, // O
+  false, // P
+  false, // Q
+  false, // R
+  false, // S
+  false, // T
+  false, // U
+  false, // V
+  false, // W
+  false, // X
+  false, // Y
+  false, // Z
+  true, //  [
+  true, //  \
+  true, //  ]
+  true, //  ^
+  false, // _
+  true, //  `
+  false, // a
+  false, // b
+  false, // c
+  false, // d
+  false, // e
+  false, // f
+  false, // g
+  false, // h
+  false, // i
+  false, // j
+  false, // k
+  false, // l
+  false, // m
+  false, // n
+  false, // o
+  false, // p
+  false, // q
+  false, // r
+  false, // s
+  false, // t
+  false, // u
+  false, // v
+  false, // w
+  false, // x
+  false, // y
+  false, // z
+  true, //  {
+  true, //  |
+  true, //  }
+  false, // ~
+  true, //  DEL
+];
+
+_parsePackagesFile(bool traceLoading, Uri packagesFile, List<int> data) {
+  // The first entry contains the location of the identified .packages file
+  // instead of a mapping.
+  var result = [packagesFile.toString(), null];
+  var index = 0;
+  var len = data.length;
+  while (index < len) {
+    var start = index;
+    var char = data[index];
+    if ((char == _CR) || (char == _LF)) {
+      // Skipping empty lines.
+      index++;
+      continue;
+    }
+
+    // Identify split within the line and end of the line.
+    var separator = -1;
+    var end = len;
+    // Verifying validity of package name while scanning the line.
+    var nonDot = false;
+    var invalidPackageName = false;
+
+    // Scan to the end of the line or data.
+    while (index < len) {
+      char = data[index++];
+      // If we have not reached the separator yet, determine whether we are
+      // scanning legal package name characters.
+      if (separator == -1) {
+        if ((char == _COLON)) {
+          // The first colon on a line is the separator between package name and
+          // related URI.
+          separator = index - 1;
+        } else {
+          // Still scanning the package name part. Check for the validity of
+          // the characters.
+          nonDot = nonDot || (char != _DOT);
+          invalidPackageName = invalidPackageName ||
+              (char < _SPACE) ||
+              (char > _DEL) ||
+              _invalidPackageNameChars[char - _SPACE];
+        }
+      }
+      // Identify end of line.
+      if ((char == _CR) || (char == _LF)) {
+        end = index - 1;
+        break;
+      }
+    }
+
+    // No further handling needed for comment lines.
+    if (data[start] == _HASH) {
+      if (traceLoading) {
+        _log("Skipping comment in $packagesFile:\n"
+            "${new String.fromCharCodes(data, start, end)}");
+      }
+      continue;
+    }
+
+    // Check for a badly formatted line, starting with a ':'.
+    if (separator == start) {
+      var line = new String.fromCharCodes(data, start, end);
+      if (traceLoading) {
+        _log("Line starts with ':' in $packagesFile:\n"
+            "$line");
+      }
+      return "Missing package name in $packagesFile:\n"
+          "$line";
+    }
+
+    // Ensure there is a separator on the line.
+    if (separator == -1) {
+      var line = new String.fromCharCodes(data, start, end);
+      if (traceLoading) {
+        _log("Line has no ':' in $packagesFile:\n"
+            "$line");
+      }
+      return "Missing ':' separator in $packagesFile:\n"
+          "$line";
+    }
+
+    var packageName = new String.fromCharCodes(data, start, separator);
+
+    // Check for valid package name.
+    if (invalidPackageName || !nonDot) {
+      var line = new String.fromCharCodes(data, start, end);
+      if (traceLoading) {
+        _log("Invalid package name $packageName in $packagesFile");
+      }
+      return "Invalid package name '$packageName' in $packagesFile:\n"
+          "$line";
+    }
+
+    if (traceLoading) {
+      _log("packageName: $packageName");
+    }
+    var packageUri = new String.fromCharCodes(data, separator + 1, end);
+    if (traceLoading) {
+      _log("original packageUri: $packageUri");
+    }
+    // Ensure the package uri ends with a /.
+    if (!packageUri.endsWith("/")) {
+      packageUri = "$packageUri/";
+    }
+    packageUri = packagesFile.resolve(packageUri).toString();
+    if (traceLoading) {
+      _log("mapping: $packageName -> $packageUri");
+    }
+    result.add(packageName);
+    result.add(packageUri);
+  }
+
+  if (traceLoading) {
+    _log("Parsed packages file at $packagesFile. Sending:\n$result");
+  }
+  return result;
+}
+
+_loadPackagesFile(bool traceLoading, Uri packagesFile) {
+  try {
+    var data = new File.fromUri(packagesFile).readAsBytesSync();
+    if (traceLoading) {
+      _log("Loaded packages file from $packagesFile:\n"
+          "${new String.fromCharCodes(data)}");
+    }
+    return _parsePackagesFile(traceLoading, packagesFile, data);
+  } catch (e, s) {
+    if (traceLoading) {
+      _log("Error loading packages: $e\n$s");
+    }
+    return "Uncaught error ($e) loading packages file.";
+  }
+}
+
+_findPackagesFile(bool traceLoading, Uri base) {
+  try {
+    // Walk up the directory hierarchy to check for the existence of
+    // .packages files in parent directories and for the existence of a
+    // packages/ directory on the first iteration.
+    var dir = new File.fromUri(base).parent;
+    var prev = null;
+    // Keep searching until we reach the root.
+    while ((prev == null) || (prev.path != dir.path)) {
+      // Check for the existence of a .packages file and if it exists try to
+      // load and parse it.
+      var dirUri = dir.uri;
+      var packagesFile = dirUri.resolve(".packages");
+      if (traceLoading) {
+        _log("Checking for $packagesFile file.");
+      }
+      var exists = new File.fromUri(packagesFile).existsSync();
+      if (traceLoading) {
+        _log("$packagesFile exists: $exists");
+      }
+      if (exists) {
+        _loadPackagesFile(traceLoading, packagesFile);
+        return;
+      }
+      // Move up one level.
+      prev = dir;
+      dir = dir.parent;
+    }
+
+    // No .packages file was found.
+    if (traceLoading) {
+      _log("Could not resolve a package location from $base");
+    }
+    return "Could not resolve a package location for base at $base";
+  } catch (e, s) {
+    if (traceLoading) {
+      _log("Error loading packages: $e\n$s");
+    }
+    return "Uncaught error ($e) loading packages file.";
+  }
+}
+
+_loadPackagesData(traceLoading, resource) {
+  try {
+    var data = resource.data;
+    var mime = data.mimeType;
+    if (mime != "text/plain") {
+      throw "MIME-type must be text/plain: $mime given.";
+    }
+    var charset = data.charset;
+    if ((charset != "utf-8") && (charset != "US-ASCII")) {
+      // The C++ portion of the embedder assumes UTF-8.
+      throw "Only utf-8 or US-ASCII encodings are supported: $charset given.";
+    }
+    return _parsePackagesFile(traceLoading, resource, data.contentAsBytes());
+  } catch (e) {
+    return "Uncaught error ($e) loading packages data.";
+  }
+}
+
+_handlePackagesRequest(bool traceLoading, int tag, Uri resource) {
+  try {
+    if (tag == -1) {
+      if (resource.scheme == '' || resource.scheme == 'file') {
+        return _findPackagesFile(traceLoading, resource);
+      } else {
+        return "Unsupported scheme used to locate .packages file:'$resource'.";
+      }
+    } else if (tag == -2) {
+      if (traceLoading) {
+        _log("Handling load of packages map: '$resource'.");
+      }
+      if (resource.scheme == '' || resource.scheme == 'file') {
+        var exists = new File.fromUri(resource).existsSync();
+        if (exists) {
+          return _loadPackagesFile(traceLoading, resource);
+        } else {
+          return "Packages file '$resource' not found.";
+        }
+      } else if (resource.scheme == 'data') {
+        return _loadPackagesData(traceLoading, resource);
+      } else {
+        return "Unknown scheme (${resource.scheme}) for package file at "
+            "'$resource'.";
+      }
+    } else {
+      return "Unknown packages request tag: $tag for '$resource'.";
+    }
+  } catch (e, s) {
+    if (traceLoading) {
+      _log("Error handling packages request: $e\n$s");
+    }
+    return "Uncaught error ($e) handling packages request.";
+  }
+}
+
+// Embedder Entrypoint:
+// The embedder calls this method to initial the package resolution state.
+@pragma("vm:entry-point")
+void _Init(String packagesConfig, String workingDirectory, String rootScript) {
+  // Register callbacks and hooks with the rest of core libraries.
+  _setupHooks();
+
+  // _workingDirectory must be set first.
+  _workingDirectory = new Uri.directory(workingDirectory);
+
+  // setup _rootScript.
+  if (rootScript != null) {
+    _rootScript = Uri.parse(rootScript);
+  }
+
+  // If the --packages flag was passed, setup _packagesConfig.
+  if (packagesConfig != null) {
+    _packageMap = null;
+    _setPackagesConfig(packagesConfig);
   }
-  return uri;
 }
 
 // Embedder Entrypoint:
@@ -224,11 +652,14 @@ Future<Uri> _getPackageConfigFuture() {
   if (_traceLoading) {
     _log("Request for package config from user code.");
   }
-  assert(_loadPort != null);
-  return _makeLoaderRequest<Uri>(_Dart_kGetPackageConfigUri, null);
+  if (!_packagesReady) {
+    _requestPackagesMap(_packagesConfigUri);
+  }
+  // Respond with the packages config (if any) after package resolution.
+  return Future.value(_packageConfig);
 }
 
-Future<Uri> _resolvePackageUriFuture(Uri packageUri) async {
+Future<Uri> _resolvePackageUriFuture(Uri packageUri) {
   if (_traceLoading) {
     _log("Request for package Uri resolution from user code: $packageUri");
   }
@@ -237,18 +668,22 @@ Future<Uri> _resolvePackageUriFuture(Uri packageUri) async {
       _log("Non-package Uri, returning unmodified: $packageUri");
     }
     // Return the incoming parameter if not passed a package: URI.
-    return packageUri;
+    return Future.value(packageUri);
   }
-  var result = await _makeLoaderRequest<Uri>(
-      _Dart_kResolvePackageUri, packageUri.toString());
-  if (result is! Uri) {
+  if (!_packagesReady) {
+    _requestPackagesMap(_packagesConfigUri);
+  }
+  Uri resolvedUri;
+  try {
+    resolvedUri = _resolvePackageUri(packageUri);
+  } catch (e, s) {
     if (_traceLoading) {
       _log("Exception when resolving package URI: $packageUri");
     }
-    result = null;
+    resolvedUri = null;
   }
   if (_traceLoading) {
-    _log("Resolved '$packageUri' to '$result'");
+    _log("Resolved '$packageUri' to '$resolvedUri'");
   }
-  return result;
+  return Future.value(resolvedUri);
 }