Reland "[ VM / DDS / CLI ] Add DevTools support to the standalone VM"

This reverts commit 5cbf10febe.

TEST=pkg/dds/devtools_observatory_connection_test.dart

Change-Id: I682d009f784b930094dae9b7d4e9a66efffb6ee8
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/198561
Reviewed-by: Siva Annamalai <asiva@google.com>

utils/dartdev/BUILD.gn

@@ -2,12 +2,14 @@
 # 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.
 
+import("../../build/dart/copy_tree.gni")
 import("../application_snapshot.gni")
 
 group("dartdev") {
   public_deps = [
     ":copy_dartdev_kernel",
     ":copy_dartdev_snapshot",
+    ":copy_prebuilt_devtools",
   ]
 }
 
@@ -39,3 +41,15 @@ application_snapshot("generate_dartdev_snapshot") {
   deps = [ "../dds:dds" ]
   output = "$root_gen_dir/dartdev.dart.snapshot"
 }
+
+copy_trees("copy_prebuilt_devtools") {
+  sources = [
+    {
+      target = "copy_prebuilt_devtools"
+      visibility = [ ":dartdev" ]
+      source = "../../third_party/devtools/web"
+      dest = "$root_out_dir/devtools"
+      ignore_patterns = "{}"
+    },
+  ]
+}