Commit Graph

27 Commits

Author SHA1 Message Date
Alexander Aprelev 0425997b31 Second attempt to reland "[vm/concurrency] Introduce concept of Isolate Groups"
This reverts commit 3d14b75f97.

An Isolate Group (IG) is a collection of isolates which were spawned from the
same source. This allows the VM to:

  * have a guarantee that all isolates within one IG can safely exchange
    structured objects (currently we rely on embedder for this
    guarantee)

  * hot-reload all isolates together (currently we only reload one
    isolate, leaving same-source isolates in inconsistent state)

  * make a shared heap for all isolates from the same IG, which paves
    the way for faster communication and sharing of immutable objects.

All isolates within one IG will share the same IsolateGroupSource.

**Embedder changes**

This change makes breaking embedder API changes to support this new
concept of Isolate Groups: The existing isolate lifecycle callbacks
given to Dart_Initialize will become Isolate Group lifecycle callbacks.
A new callback `initialize_isolate` callback will be added which can
initialize a new isolate within an existing IG.

Existing embedders can be updated by performing the following renames

  Dart_CreateIsolate -> Dart_CreateIsolateGroup
  Dart_IsolateCreateCallback -> Dart_IsolateGroupCreateCallback
  Dart_IsolateCleanupCallback -> Dart_IsolateGroupShutdownCallback
  Dart_CreateIsolateFromKernel -> Dart_CreateIsolateGroupFromKernel
  Dart_CurrentIsolateData -> Dart_CurrentIsolateGroupData
  Dart_IsolateData -> Dart_IsolateGroupData
  Dart_GetNativeIsolateData -> Dart_GetNativeIsolateGroupData
  Dart_InitializeParams.create -> Dart_InitializeParams.create_group
  Dart_InitializeParams.cleanup -> Dart_InitializeParams.shutdown_group
  Dart_InitializeParams.shutdown -> Dart_InitializeParams.shutdown_isolate

By default `Isolate.spawn` will cause the creation of a new IG.

Though an embedder can opt-into supporting multiple isolates within one IG by
providing a callback to the newly added `Dart_InitializeParams.initialize_isolate`.
The responsibility of this new callback is to initialize an existing
isolate (which was setup by re-using source code from the spawning
isolate - i.e. the one which used `Isolate.spawn`) by setting native
resolvers, initializing global state, etc.

Issue https://github.com/dart-lang/sdk/issues/36648
Issue https://github.com/dart-lang/sdk/issues/36097

Original review: https://dart-review.googlesource.com/c/sdk/+/105241

Difference to original review:

  * Give each isolate it's own [Loader] (for now)
  * Sort classes during initialization for spawned isolates if app-jit is used (to match main isolate)
  * Fix IsolateData memory leak if isolate startup fails

Difference to first reland(Patchset 2):

  * Fix typo where memory was freed twice.

Change-Id: Ib1c83fe83b629cd50ae6af90ee99fdd44da882d4
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/108367
Commit-Queue: Alexander Aprelev <aam@google.com>
Reviewed-by: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
2019-07-08 23:49:05 +00:00
Vyacheslav Egorov 3d14b75f97 Revert "Reland "[vm/concurrency] Introduce concept of Isolate Groups""
This reverts commit 67ab3be10d.

Reason for revert: Causes non-deterministic failures on front-end bots on Windows with "Isolate creation failed" error. See https://logs.chromium.org/logs/dart/buildbucket/cr-buildbucket.appspot.com/8909292129328681248/+/steps/unit_tests/0/stdout

Original change's description:
> Reland "[vm/concurrency] Introduce concept of Isolate Groups"
> 
> An Isolate Group (IG) is a collection of isolates which were spawned from the
> same source. This allows the VM to:
> 
>   * have a guarantee that all isolates within one IG can safely exchange
>     structured objects (currently we rely on embedder for this
>     guarantee)
> 
>   * hot-reload all isolates together (currently we only reload one
>     isolate, leaving same-source isolates in inconsistent state)
> 
>   * make a shared heap for all isolates from the same IG, which paves
>     the way for faster communication and sharing of immutable objects.
> 
> All isolates within one IG will share the same IsolateGroupSource.
> 
> **Embedder changes**
> 
> This change makes breaking embedder API changes to support this new
> concept of Isolate Groups: The existing isolate lifecycle callbacks
> given to Dart_Initialize will become Isolate Group lifecycle callbacks.
> A new callback `initialize_isolate` callback will be added which can
> initialize a new isolate within an existing IG.
> 
> Existing embedders can be updated by performing the following renames
> 
>   Dart_CreateIsolate -> Dart_CreateIsolateGroup
>   Dart_IsolateCreateCallback -> Dart_IsolateGroupCreateCallback
>   Dart_IsolateCleanupCallback -> Dart_IsolateGroupShutdownCallback
>   Dart_CreateIsolateFromKernel -> Dart_CreateIsolateGroupFromKernel
>   Dart_CurrentIsolateData -> Dart_CurrentIsolateGroupData
>   Dart_IsolateData -> Dart_IsolateGroupData
>   Dart_GetNativeIsolateData -> Dart_GetNativeIsolateGroupData
>   Dart_InitializeParams.create -> Dart_InitializeParams.create_group
>   Dart_InitializeParams.cleanup -> Dart_InitializeParams.shutdown_group
>   Dart_InitializeParams.shutdown -> Dart_InitializeParams.shutdown_isolate
> 
> By default `Isolate.spawn` will cause the creation of a new IG.
> 
> Though an embedder can opt-into supporting multiple isolates within one IG by
> providing a callback to the newly added `Dart_InitializeParams.initialize_isolate`.
> The responsibility of this new callback is to initialize an existing
> isolate (which was setup by re-using source code from the spawning
> isolate - i.e. the one which used `Isolate.spawn`) by setting native
> resolvers, initializing global state, etc.
> 
> Issue https://github.com/dart-lang/sdk/issues/36648
> Issue https://github.com/dart-lang/sdk/issues/36097
> 
> Original review: https://dart-review.googlesource.com/c/sdk/+/105241
> 
> Difference to original review:
> 
>   * Give each isolate it's own [Loader] (for now)
>   * Sort classes during initialization for spawned isolates if app-jit is used (to match main isolate)
>   * Fix IsolateData memory leak if isolate startup fails
> 
> Change-Id: I98277d3d10fe275aa9b8a16b6bdd446bbea0b100
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107506
> Commit-Queue: Martin Kustermann <kustermann@google.com>
> Reviewed-by: Ryan Macnak <rmacnak@google.com>

TBR=kustermann@google.com,aam@google.com,rmacnak@google.com

# Not skipping CQ checks because original CL landed > 1 day ago.

Change-Id: Ia4e0f4f9fc317499d3570a371c5bdf9aed799e77
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/108101
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
Commit-Queue: Vyacheslav Egorov <vegorov@google.com>
2019-07-03 12:19:15 +00:00
Martin Kustermann 67ab3be10d Reland "[vm/concurrency] Introduce concept of Isolate Groups"
An Isolate Group (IG) is a collection of isolates which were spawned from the
same source. This allows the VM to:

  * have a guarantee that all isolates within one IG can safely exchange
    structured objects (currently we rely on embedder for this
    guarantee)

  * hot-reload all isolates together (currently we only reload one
    isolate, leaving same-source isolates in inconsistent state)

  * make a shared heap for all isolates from the same IG, which paves
    the way for faster communication and sharing of immutable objects.

All isolates within one IG will share the same IsolateGroupSource.

**Embedder changes**

This change makes breaking embedder API changes to support this new
concept of Isolate Groups: The existing isolate lifecycle callbacks
given to Dart_Initialize will become Isolate Group lifecycle callbacks.
A new callback `initialize_isolate` callback will be added which can
initialize a new isolate within an existing IG.

Existing embedders can be updated by performing the following renames

  Dart_CreateIsolate -> Dart_CreateIsolateGroup
  Dart_IsolateCreateCallback -> Dart_IsolateGroupCreateCallback
  Dart_IsolateCleanupCallback -> Dart_IsolateGroupShutdownCallback
  Dart_CreateIsolateFromKernel -> Dart_CreateIsolateGroupFromKernel
  Dart_CurrentIsolateData -> Dart_CurrentIsolateGroupData
  Dart_IsolateData -> Dart_IsolateGroupData
  Dart_GetNativeIsolateData -> Dart_GetNativeIsolateGroupData
  Dart_InitializeParams.create -> Dart_InitializeParams.create_group
  Dart_InitializeParams.cleanup -> Dart_InitializeParams.shutdown_group
  Dart_InitializeParams.shutdown -> Dart_InitializeParams.shutdown_isolate

By default `Isolate.spawn` will cause the creation of a new IG.

Though an embedder can opt-into supporting multiple isolates within one IG by
providing a callback to the newly added `Dart_InitializeParams.initialize_isolate`.
The responsibility of this new callback is to initialize an existing
isolate (which was setup by re-using source code from the spawning
isolate - i.e. the one which used `Isolate.spawn`) by setting native
resolvers, initializing global state, etc.

Issue https://github.com/dart-lang/sdk/issues/36648
Issue https://github.com/dart-lang/sdk/issues/36097

Original review: https://dart-review.googlesource.com/c/sdk/+/105241

Difference to original review:

  * Give each isolate it's own [Loader] (for now)
  * Sort classes during initialization for spawned isolates if app-jit is used (to match main isolate)
  * Fix IsolateData memory leak if isolate startup fails

Change-Id: I98277d3d10fe275aa9b8a16b6bdd446bbea0b100
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107506
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
2019-06-29 18:45:11 +00:00
Martin Kustermann b2171f16f1 Revert "[vm/concurrency] Introduce concept of Isolate Groups"
This reverts commit b75057b687.

Reason for revert: Caused some failures on app-jit builders

Original change's description:
> [vm/concurrency] Introduce concept of Isolate Groups
> 
> An Isolate Group (IG) is a collection of isolates which were spawned from the
> same source. This allows the VM to:
> 
>   * have a guarantee that all isolates within one IG can safely exchange
>     structured objects (currently we rely on embedder for this
>     guarantee)
> 
>   * hot-reload all isolates together (currently we only reload one
>     isolate, leaving same-source isolates in inconsistent state)
> 
>   * make a shared heap for all isolates from the same IG, which paves
>     the way for faster communication and sharing of immutable objects.
> 
> All isolates within one IG will share the same IsolateGroupSource.
> 
> **Embedder changes**
> 
> This change makes breaking embedder API changes to support this new
> concept of Isolate Groups: The existing isolate lifecycle callbacks
> given to Dart_Initialize will become Isolate Group lifecycle callbacks.
> A new callback `initialize_isolate` callback will be added which can
> initialize a new isolate within an existing IG.
> 
> Existing embedders can be updated by performing the following renames
> 
>   Dart_CreateIsolate -> Dart_CreateIsolateGroup
>   Dart_IsolateCreateCallback -> Dart_IsolateGroupCreateCallback
>   Dart_IsolateCleanupCallback -> Dart_IsolateGroupShutdownCallback
>   Dart_CreateIsolateFromKernel -> Dart_CreateIsolateGroupFromKernel
>   Dart_CurrentIsolateData -> Dart_CurrentIsolateGroupData
>   Dart_IsolateData -> Dart_IsolateGroupData
>   Dart_GetNativeIsolateData -> Dart_GetNativeIsolateGroupData
>   Dart_InitializeParams.create -> Dart_InitializeParams.create_group
>   Dart_InitializeParams.cleanup -> Dart_InitializeParams.shutdown_group
>   Dart_InitializeParams.shutdown -> Dart_InitializeParams.shutdown_isolate
> 
> By default `Isolate.spawn` will cause the creation of a new IG.
> 
> Though an embedder can opt-into supporting multiple isolates within one IG by
> providing a callback to the newly added `Dart_InitializeParams.initialize_isolate`.
> The responsibility of this new callback is to initialize an existing
> isolate (which was setup by re-using source code from the spawning
> isolate - i.e. the one which used `Isolate.spawn`) by setting native
> resolvers, initializing global state, etc.
> 
> Issue https://github.com/dart-lang/sdk/issues/36648
> Issue https://github.com/dart-lang/sdk/issues/36097
> 
> Change-Id: I82437ac017ca33018d45e02f353b0672db155f6a
> Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/105241
> Commit-Queue: Martin Kustermann <kustermann@google.com>
> Reviewed-by: Ryan Macnak <rmacnak@google.com>
> Reviewed-by: Alexander Aprelev <aam@google.com>

TBR=kustermann@google.com,aam@google.com,rmacnak@google.com

Change-Id: Ibd90992a01d61188f27b445c21532e0c46f996ea
No-Presubmit: true
No-Tree-Checks: true
No-Try: true
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/107405
Reviewed-by: Martin Kustermann <kustermann@google.com>
Commit-Queue: Martin Kustermann <kustermann@google.com>
2019-06-26 16:04:27 +00:00
Martin Kustermann b75057b687 [vm/concurrency] Introduce concept of Isolate Groups
An Isolate Group (IG) is a collection of isolates which were spawned from the
same source. This allows the VM to:

  * have a guarantee that all isolates within one IG can safely exchange
    structured objects (currently we rely on embedder for this
    guarantee)

  * hot-reload all isolates together (currently we only reload one
    isolate, leaving same-source isolates in inconsistent state)

  * make a shared heap for all isolates from the same IG, which paves
    the way for faster communication and sharing of immutable objects.

All isolates within one IG will share the same IsolateGroupSource.

**Embedder changes**

This change makes breaking embedder API changes to support this new
concept of Isolate Groups: The existing isolate lifecycle callbacks
given to Dart_Initialize will become Isolate Group lifecycle callbacks.
A new callback `initialize_isolate` callback will be added which can
initialize a new isolate within an existing IG.

Existing embedders can be updated by performing the following renames

  Dart_CreateIsolate -> Dart_CreateIsolateGroup
  Dart_IsolateCreateCallback -> Dart_IsolateGroupCreateCallback
  Dart_IsolateCleanupCallback -> Dart_IsolateGroupShutdownCallback
  Dart_CreateIsolateFromKernel -> Dart_CreateIsolateGroupFromKernel
  Dart_CurrentIsolateData -> Dart_CurrentIsolateGroupData
  Dart_IsolateData -> Dart_IsolateGroupData
  Dart_GetNativeIsolateData -> Dart_GetNativeIsolateGroupData
  Dart_InitializeParams.create -> Dart_InitializeParams.create_group
  Dart_InitializeParams.cleanup -> Dart_InitializeParams.shutdown_group
  Dart_InitializeParams.shutdown -> Dart_InitializeParams.shutdown_isolate

By default `Isolate.spawn` will cause the creation of a new IG.

Though an embedder can opt-into supporting multiple isolates within one IG by
providing a callback to the newly added `Dart_InitializeParams.initialize_isolate`.
The responsibility of this new callback is to initialize an existing
isolate (which was setup by re-using source code from the spawning
isolate - i.e. the one which used `Isolate.spawn`) by setting native
resolvers, initializing global state, etc.

Issue https://github.com/dart-lang/sdk/issues/36648
Issue https://github.com/dart-lang/sdk/issues/36097

Change-Id: I82437ac017ca33018d45e02f353b0672db155f6a
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/105241
Commit-Queue: Martin Kustermann <kustermann@google.com>
Reviewed-by: Ryan Macnak <rmacnak@google.com>
Reviewed-by: Alexander Aprelev <aam@google.com>
2019-06-26 11:34:48 +00:00
Matthew Dempsky 6d5f763952 [vm] Eliminate Mutex/Monitor indirection where possible
In many cases, the Mutexes and Monitors have to be marked "mutable"
because they're used to synchronize const accessor methods.

Small text segment improvement for Product builds:

$ size dart.{arm,x64}.{before,after}
   text	   data	    bss	    dec	    hex	filename
19726069	 409960	 392332	20528361	1393ce9	dart.arm.before
19725525	 409960	 392332	20527817	1393ac9	dart.arm.after
22576021	 600376	1782824	24959221	17cd8f5	dart.x64.before
22574821	 600376	1782824	24958021	17cd445	dart.x64.after

Change-Id: I68f5cd5ad452044df8bfebd160910496036a3e6b
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/101745
Commit-Queue: Matthew Dempsky <mdempsky@google.com>
Reviewed-by: Vyacheslav Egorov <vegorov@google.com>
2019-05-13 21:17:51 +00:00
Siva Chandra 71dba8a0e5 Link the platform kernel with the command line dart executable.
Change-Id: Ib376a259e2e9ff9b487820c041d6795f8f7192d1
Reviewed-on: https://dart-review.googlesource.com/37420
Reviewed-by: Siva Annamalai <asiva@google.com>
Commit-Queue: Siva Chandra <sivachandra@google.com>
2018-02-01 15:11:29 +00:00
Zachary Anderson 6cd8a79078 VM: Re-format to use at most one newline between functions
R=asiva@google.com

Review-Url: https://codereview.chromium.org/2974233002 .
2017-07-13 08:08:37 -07:00
Ryan Macnak 06080dae96 Fix some assertion failures on Fuchsia
- Fix longjmp asserts to work with -fsanitize=safe-stack.
 - Remove outdated asserts in gen_snapshot assuming generation of a core snapshot.
 - Move depfile resolution so it happens outside of the tag handler.

Issue #29458

R=asiva@google.com, johnmccutchan@google.com, zra@google.com

Review-Url: https://codereview.chromium.org/2837873005 .
2017-04-26 15:34:31 -07:00
P.Y. Laligand 8f03520d2b New dart CLI option to create a snapshot depfile. (#29165) 2017-03-27 06:44:21 -07:00
Ryan Macnak 781fd36086 Add an option to gen_snapshot for creating a Makefile describing a snapshot's dependencies. This option may be used when generating any snapshot kind, or without generating a snapshot.
- Factor out MallocGrowableArray from vm to platform.
 - Add File::Print.

R=asiva@google.com

Review-Url: https://codereview.chromium.org/2715463003 .
2017-02-23 12:40:48 -08:00
Vyacheslav Egorov 9bae50bf47 VM: [Kernel] Revert changes to the native ports that introduced peers.
The problem with these changes was that closed ports still continue to receive
messages and as a result we start using dead peer objects.

Fixing that would require more intrusive changes into message handler implementation - so instead we are reverting the changes and restoring manual PORT -> PEER mapping.

BUG=
R=erikcorry@google.com

Review-Url: https://codereview.chromium.org/2666063002 .
2017-01-31 10:30:15 +01:00
Vyacheslav Egorov 43a0500e37 VM: [Kernel] Fix bootstraping when Kernel isolate is used.
We must bootstrap from Kernel instead of Source when running with --dfe

BUG=
R=asiva@google.com, kustermann@google.com

Review-Url: https://codereview.chromium.org/2651633002 .
2017-01-30 20:52:59 +01:00
Matthias Hausner f5ab173c77 Add Kernel Isolate, second attempt
To run a script with the Dart->Kernel parser, use the -dfe option:

dart --dfe=runtime/tools/kernel-service.dart  --packages=/src/d2/sdk/.packages  foo.dart

The front end expects a directory named patched_sdk in the build directory (patched_sdk should be a sibling of the directory that contains the dart executable.)

Warning: using a debug build dart executable is very slow. It takes 2 minutes to run Hello World in a debug build, and about 7 seconds in a release build.

BUG=
R=asiva@google.com

Review URL: https://codereview.chromium.org/2558673002 .
2016-12-07 09:11:16 -08:00
Matthias Hausner 2ea399285a Revert "Add Kernel Isolate"
This reverts commit c9399fc557.

The change broke Dartium and Fuchsia.

BUG=

Review URL: https://codereview.chromium.org/2554953004 .
2016-12-06 14:17:09 -08:00
Matthias Hausner c9399fc557 Add Kernel Isolate
To run a script with the Dart->Kernel parser, use the -dfe option:

dart --dfe=runtime/tools/kernel-service.dart  --packages=/src/d2/sdk/.packages  foo.dart

The front end expects a directory named patched_sdk in the build directory (patched_sdk should be a sibling of the directory that contains the dart executable.)

Warning: using a debug build dart executable is very slow. It takes 2 minutes to run Hello World in a debug build, and about 7 seconds in a release build.

BUG=
R=asiva@google.com

Review URL: https://codereview.chromium.org/2483373002 .
2016-12-06 12:23:09 -08:00
Ryan Macnak 987165f022 Reload native extensions when starting from a snapshot.
Fixes #21180
Fixes #27574

R=johnmccutchan@google.com

Review URL: https://codereview.chromium.org/2475523002 .
2016-11-07 16:17:47 -08:00
Zachary Anderson 479a97b129 clang-format runtime/bin
R=johnmccutchan@google.com

Review URL: https://codereview.chromium.org/2480793002 .
2016-11-04 12:30:56 -07:00
Zachary Anderson 103881d01c Make header include guards great again
i.e. #ifndef VM_WHATEVER -> #ifndef RUNTIME_VM_WHATEVER

This lets us remove a hack from the PRESUBMIT.py script that existed
for reasons that are no longer valid, and sets us up to add some
presubmit checks for the GN build.

R=asiva@google.com, rmacnak@google.com

Review URL: https://codereview.chromium.org/2450713004 .
2016-10-26 00:26:03 -07:00
Todd Turnidge 1166f83bf6 Only reload libraries when they may have been modified.
We now check all of the scripts which make up a library.  If any
script is modified, then we consider that library to be modified.  We
also consider any library which imports a modified library to be
modified.  To propagate this info efficiently, we build and discard
the imported-by graph when beginning a reload.

The embedder must provide a FileModifiedCallback in order to support
the detection of modified scripts.

In order to detect changes to package: libraries, we have modified the
embedder interface to provide the resolved url when possible, so that
we don't need to re-resolve package uris when checking for reload.
This change is incompatible and all embedders will need to be updated.

We now support a "force" flag when reloading sources.  This causes all
libraries to be reloaded regardless of whether the underlying scripts
have been updated.

Closes #26919

R=johnmccutchan@google.com

Review URL: https://codereview.chromium.org/2186423002 .
2016-07-29 11:23:18 -07:00
John McCutchan 05c1eac65d Support loading dart-ext from within a package when using a package map
Fixes https://github.com/dart-lang/sdk/issues/26879

When a dart-ext is imported from within a package: library we need to fully resolve the package: to a file: (or whatever scheme:) so that we can locate the shared object for the extension file.

This CL sends this request through the service isolate so that the package: can be resolved even when a package config is being used.

R=asiva@google.com

Review URL: https://codereview.chromium.org/2146093002 .
2016-07-13 15:20:13 -07:00
Florian Schneider 63e3f4dc8b Make loader lock new-allocated to avoid shutdown crash.
Process::Exit does not do the normal shutdown procedure - this CL avoids
a crash in the static destructor of the loader info lock by making it
new-allocated.

Also remove --shutdown flag since the clean shutdown procedure is on by
default since a while now.

BUG=#26846
R=asiva@google.com, zra@google.com

Review URL: https://codereview.chromium.org/2147833002 .
2016-07-13 09:41:06 -07:00
Siva Annamalai 11682cd4c7 Use the new loader mechanism to resolve URIs and load script files in gen_snapshot. This should allow the package config resolution to work in gen_snapshot for flutter and dartium snapshot generation cases.
R=johnmccutchan@google.com

Review URL: https://codereview.chromium.org/2073173002 .
2016-06-20 13:56:06 -07:00
John McCutchan 3b2e14ab56 Fix deferred load errors
R=hausner@google.com

Review URL: https://codereview.chromium.org/2045023003 .
2016-06-08 07:12:52 -07:00
John McCutchan bf4b3b3733 Activate the service isolate for all precompiled tests.
- [x] We always need the load port now.
- [x] Fix a minor locking issue in Loader::~Loader

BUG=
R=rmacnak@google.com

Review URL: https://codereview.chromium.org/2041113003 .
2016-06-07 12:47:44 -07:00
John McCutchan 1020392647 Add missing locking around loaders list
BUG=

Review URL: https://codereview.chromium.org/2039383002 .
2016-06-06 14:51:24 -07:00
John McCutchan 6fd8fd7987 Rework standalone to use a synchronous loader that does not invoke Dart code
- [x] The first caller of the tag handler blocks, recursive callers queue work and exit.
- [x] Use a NativeMessageHandler to receive I/O results from the service isolate.
- [x] Preserve load error message format.
- [x] Move packages map into service isolate.
- [x] Wire up Todd's native URI code.

R=turnidge@google.com

Review URL: https://codereview.chromium.org/1998963003 .
2016-06-06 14:15:01 -07:00