- Add missing Dart 2 flags to gen_snapshot invocation.
 - Disable brittle service test.

This reverts commit 4c2448d1.

 - Switch core snapshot to Dart 2 and remove support for loading platform.dill.
 - Remove support for loading script snapshots.
 - Remove support for loading source.
 - Remove settings and fix names to reflect the above.
 - Remove support for loading the service isolate from source.

* Roll dart sdk to 4c9689c1d2da97d0aa25cf16cc90c2e463ad157f

Changes since last roll:
```
4c9689c1d2 [vm] Support pluggable expression compiler for `evaluate` service api call.
d70c38eed8 [Gardening] Mark test as flaky on also non-kernel (legacy)
060ee6769e Make CastStreamSubscription.onData handle a null callback
f7289aa219 Remove specification of naming conventions.
87131780cb Add appendix to spec which specifies JavaScript integer behavior.
dfeaf79cef Fix VM accepting too many overlarge hex numbers in int.parse.
c84a9f46b2 Recompute ClassHierarchy after adding noSuchMethod forwarding stubs
b558a9c2f4 Handle missing compile-time errors
3df126c497 [gardening] Update status for vm-kernel-linux-debug
e22706793d Treat objects with .call as "subtypes" of function types
b960e5a3ed [gardening] Mark standalone_2/io/directory_test as Crash on dartkp/debug
e2d72aad91 Prepare tools/bots/try_benchmarks.sh for Dart 2.
de5f9ea95f Add --use-fasta-parser flags to dartanalyzer and the analysis server.
e2d903c4dc Remove packages/ directory resolution from CFE
aabb78f56a Update checked-in SDK to 2.0.0-dev.63.0 on mac and linux.
bc8d77231d Improve flags documentation, reenable hints in dart2js.
209a602769 Tweak for fixes tests - use orElse to avoid exception.
0e4c158847 Issue 33458. Suggest 'Create Class' Quick Fix for creation without new.
44650cc9eb Pass the location of vm_platform to compile_platform from the commandline.
0bac650833 switch to dart_action until prebuilt Windows Dart VM is updated
82ed18cdb9 Update checked-in Windows SDK to 2.0.0-dev.63.0
2394097e44 Support for including/excluding the same path in ContextRoot.isAnalyzed().
f59389b688 Optimize .runtimeType impact based on usage
ee1f7f5a93 Fix newly reported warnings
afa8ff6292 Add a resource provider that supports file overlays
a63cf8e0cb Add --no-preview-dart-2 flag.
2a396d5315 [vm/intrinsics] Intrinsify 64-bit int typed data.
dd8988c9b2 - Moved all WebGL rendering/drawing constants to synthesized class WebGL. - Removed obsolete Dartium/_blink code.
541dd195bb Enable creating full kernel files in addition to outlines from the bazel worker for kernel.
8e9e8e1da0 Fix various bugs and regularize behavior of returns statements in various kinds of functions.
f1d1da6164 [vm/precomp] Reduce the size of slow-path code in precompiled mode.
b51d3d4146 Key string should be avoided
1e906c3f7e Add no-op entry point for IncrementalCompiler
aeeb7baa96 Change error message to not use imperative tone
309baedc72 Mark some frequently flaky co19 dart2js tests.
1a08341730 Analyzer status file update
ac039abc83 Add option to check if a dill is self-contained
f479435bca - Removed custom handling of fill - it was wrong the method is now overloaded. - Associate the JS class SpeechSyntesisVoice with the correct Dart class (DDC). - Top-level querySelectorAll wasn't generic. - Handle "static" for attributes in the IDLs.
d2a37231b3 optimize await in async* methods in dartdevc
8f0106e490 Update more Analyzer fasta tests
53c2a6f9d5 Cleanup remaining unescape string call sites
1ef4399df0 Run dartfmt --fix for dart2 on pkg/dev_compiler
38eda19be6 Fix resolve_input_uri_test on windows.
5bf6436bc9 Initial implementations of two generators
03bcc495f7 [fuchsia] Migrate process creation to fdio_spawn_vmo
0cf860f361 Remove pub_build_validity test
c015e8d303 Improve invalid string literal error recovery
84f077842b Update CHANGELOG.md for 2.0.0-dev.63 release
7757fa784a [vm] Remove redundant Profiler::DumpStackTrace().
2bc9025be3 Consider initializing formals during top-level type inference
9df6426adb Mark the library analyzer.dart as being deprecated
bd956620fe Remove code that is causing a couple of hints
d99aeb3e13 [kernel] Update Fuchsia suspend to use new API.
6f44d3f208 Issue 2287. Move all, but constructors and fields set in constructors, from StatelessWidget into State.
729e9942bd Support multiple files in messages test.
99575f79ca Split ContextAwareGenerator and its subclasses
41a8b79475 Use the inferred type of const lists/maps to for constant evaluation.
2972ca61f8 Fix continue in invalidation logic
c54a302495 [VM] Evaluate symbols in kernel2kernel constant evaluator in AOT (even in non-const contexts)
4a7ccd5c9a Deleted TODO comment in Scoping
8dca855de1 Specify dynamic type of Futures/... returned from async/... functions
385d825469 Make frontend_server initialize from dill work again
2716b6f9a6 Add test to frontend_server that mimics the flutter benchmarks
17d2839a03 Fixed tests for FF difference.
6779ea0cc6 GN rules: add libraries_specification_uri argument to the  compile_platform template.
12b33ada44 [VM interpreter] Support NativeCall kernel bytecode.
db72134f90 [vm/inliner] Add smi return type of clamped convertors.
33feee3b03 [vm/kernel/bytecode] Fix arguments passing in native factory constructors
c30ce41ae6 Add hook to use single-root in fasta scripts and make use of it when creating the dart2js platform files.
34ee27a52d Update to the latest pub
bfb9a4eab8 linter 0.1.53
dfe6385eb0 Fix a Dart 2 runtime cast failure
f7ef66f5b0 Issue 33412. Fix for race condition in knownFiles during search.
aca417a256 Fix test and expected failure.
664f756914 [vm] Reduce maximum new generation size and growth rate.
bd603ba3c6 Record dependencies via CompilerContext
```

* Roll dart sdk to e6d7d67f4b35556805dd083fed15bf3ed41f7e33.

Changes since last dart roll:

```
e6d7d67f4b Revert 4f18af12c7c6d53f02cf32cb9b5ea848b86e1d77 as it causes test breakages.
4877587346 [GN] Uses dart_action.gni instead of compiled_action.gni.
4b89ba24fb Meta CHANGELOG markdown cleanup.
3d688deba7 Bump analysis server version to 1.20.2
0dc81ae4eb Publish package:meta 1.1.5
7e54844fe7 [vm] Fix build for gcc 7.3.0.
9d10a6ad4a Issue 33034. Fix statement completion with missing condition right parenthesis.
3fd2d5fb05 [vm] Use compiler warnings to insist callers check for errors from Dart_Invoke*/Load*/Compile*.
afb490adbc [dart:io] Provide modern Dart-styled constants
2929b71aa2 [kernel/vm] Address follow-up review comments for bytecode generation
73768a5342 General TypeInfo and IdentifierContext cleanup
e93b2ee250 Improve typedef identifier recovery
46a9ed0617 Added example about calling a tear-off with a wrong-shape argument list
0c839cf3f8 [fasta] Add 'as' expressions to the Forest API
16f6ce2fee [release] Prepare changelog for 2.0.0-dev.53.0
d13bf49870 Check type-variable bounds on generic methods
794fe1e14f Add stacktrace tests for synchronous async
fb779df11c [frontend-server] Disable depfile test on Windows.
```

* Adjust gn-scripts to accommodate 487758734695e7a701325b80178465ebbd0fafdd refactoring.

* Re-land "Support multiple shells in a single process. (#4932)"

This reverts commit 723c7d01.

This reverts commit a3327bff.

This reverts commit 9199b40f.

This reverts commit 6baff4c8.

* Support multiple shells in a single process.

The Flutter Engine currently works by initializing a singleton shell
instance. This shell has to be created on the platform thread. The shell
is responsible for creating the 3 main threads used by Flutter (UI, IO,
GPU) as well as initializing the Dart VM. The shell, references to task
runners of the main threads as well as all snapshots used for VM
initialization are stored in singleton objects. The Flutter shell only
creates the threads, rasterizers, contexts, etc. to fully support a
single Flutter application. Current support for multiple Flutter
applications is achieved by making multiple applications share the same
resources (via the platform views mechanism).

This scheme has the following limitations:

* The shell is a singleton and there is no way to tear it down. Once you
  run a Flutter application in a process, all resources managed by it
  will remain referenced till process termination.
* The threads on which the shell performs its operations are all
  singletons. These threads are never torn down and multiple Flutter
  applications (if present) have to compete with one another on these
  threads.
* Resources referenced by the Dart VM are leaked because the VM isn't
  shutdown even when there are no more Flutter views.
* The shell as a target does not compile on Fuchsia. The Fuchsia content
  handler uses specific dependencies of the shell to rebuild all the
  shell dependencies on its own. This leads to differences in frame
  scheduling, VM setup, service protocol endpoint setup, tracing, etc..
  Fuchsia is very much a second class citizen in this world.
* Since threads and message loops are managed by the engine, the engine
  has to know about threading and platform message loop interop on each
  supported platform.

Specific updates in this patch:

* The shell is no longer a singleton and the embedder holds the unique
  reference to the shell.
* Shell setup and teardown is deterministic.
* Threads are no longer managed by the shell. Instead, the shell is
  given a task runner configuration by the embedder.
* Since the shell does not own its threads, the embedder can control
  threads and the message loops operating on these threads. The shell is
  only given references to the task runners that execute tasks on these
  threads.
* The shell only needs task runner references. These references can be
  to the same task runner. So, if the embedder thinks that a particular
  Flutter application would not need all the threads, it can pass
  references to the same task runner. This effectively makes Flutter
  application run in single threaded mode. There are some places in the
  shell that make synchronous calls, these sites have been updated to
  ensure that they don’t deadlock.
* The test runner and the headless Dart code runner are now Flutter
  applications that are effectively single threaded (since they don’t
  have rendering concerns of big-boy Flutter application).
* The embedder has to guarantee that the threads and outlive the shell.
  It is easy for the embedder to make that guarantee because shell
  termination is deterministic.
* The embedder can create as many shell as it wants. Typically it
  creates a shell per Flutter application with its own task runner
  configuration. Most embedders obtain these task runners from threads
  dedicated to the shell. But, it is entirely possible that the embedder
  can obtain these task runners from a thread pool.
* There can only be one Dart VM in the process. The numerous shell
  interact with one another to manage the VM lifecycle. Once the last
  shell goes away, the VM does as well and hence all resources
  associated with the VM are collected.
* The shell as a target can now compile and run on Fuchsia. The current
  content handler has been removed from the Flutter engine source tree
  and a new implementation has been written that uses the new shell
  target.
* Isolate management has been significantly overhauled. There are no
  owning references to Dart isolates within the shell. The VM owns the
  only strong reference to the Dart isolate. The isolate that has window
  bindings is now called the root isolate. Child isolates can now be
  created from the root isolate and their bindings and thread
  configurations are now inherited from the root isolate.
* Terminating the shell terminates its root isolates as well as all the
  isolates spawned by this isolate. This is necessary be shell shutdown
  is deterministic and the embedder is free to collect the threads on
  which the isolates execute their tasks (and listen for mircrotasks
  flushes on).
* Launching the root isolate is now significantly overhauled. The shell
  side (non-owning) reference to an isolate is now a little state
  machine and illegal state transitions should be impossible (barring
  construction issues). This is the only way to manage Dart isolates in
  the shell (the shell does not use the C API is dart_api.h anymore).
* Once an isolate is launched, it must be prepared (and hence move to
  the ready phase) by associating a snapshot with the same. This
  snapshot can either be a precompiled snapshot, kernel snapshot, script
  snapshot or source file. Depending on the kind of data specified as a
  snapshot as well as the capabilities of the VM running in the process,
  isolate preparation can fail preparation with the right message.
* Asset management has been significantly overhauled. All asset
  resolution goes through an abstract asset resolver interface. An asset
  manager implements this interface and manages one or more child asset
  resolvers. These asset resolvers typically resolve assets from
  directories, ZIP files (legacy FLX assets if provided), APK bundles,
  FDIO namespaces, etc…
* Each launch of the shell requires a separate and fully configured
  asset resolver. This is necessary because launching isolates for the
  engine may require resolving snapshots as assets from the asset
  resolver. Asset resolvers can be shared by multiple launch instances
  in multiple shells and need to be thread safe.
* References to the command line object have been removed from the
  shell. Instead, the shell only takes a settings object that may be
  configured from the command line. This makes it easy for embedders and
  platforms that don’t have a command line (Fuchsia) to configure the
  shell. Consequently, there is only one spot where the various switches
  are read from the command line (by the embedder and not the shell) to
  form the settings object.
* All platform now respect the log tag (this was done only by Android
  till now) and each shell instance have its own log tag. This makes
  logs from multiple Flutter application in the same process (mainly
  Fuchsia) more easily decipherable.
* The per shell IO task runner now has a new component that is
  unfortunately named the IOManager. This component manages the IO
  GrContext (used for asynchronous texture uploads) that cooperates with
  the GrContext on the GPU task runner associated with the shell. The
  IOManager is also responsible for flushing tasks that collect Skia
  objects that reference GPU resources during deterministic shell
  shutdown.
* The embedder now has to be careful to only enable Blink on a single
  instance of the shell. Launching the legacy text layout and rendering
  engine multiple times is will trip assertions. The entirety of this
  runtime has been separated out into a separate object and can be
  removed in one go when the migration to libtxt is complete.
* There is a new test target for the various C++ objects that the shell
  uses to interact with the Dart VM (the shell no longer use the C API
  in dart_api.h). This allows engine developers to test VM/Isolate
  initialization and teardown without having the setup a full shell
  instance.
* There is a new test target for the testing a single shell instances
  without having to configure and launch an entire VM and associated
  root isolate.
* Mac, Linux & Windows used to have different target that created the
  flutter_tester referenced by the tool. This has now been converted
  into a single target that compiles on all platforms.
* WeakPointers vended by the fml::WeakPtrFactory(notice the difference
  between the same class in the fxl namespace) add threading checks on
  each use. This is enabled by getting rid of the “re-origination”
  feature of the WeakPtrFactory in the fxl namespace. The side effect of
  this is that all non-thread safe components have to be created, used
  and destroyed on the same thread. Numerous thread safety issues were
  caught by this extra assertion and have now been fixed.
  * Glossary of components that are only safe on a specific thread (and
    have the fml variants of the WeakPtrFactory):
    * Platform Thread: Shell
    * UI Thread: Engine, RuntimeDelegate, DartIsolate, Animator
    * GPU Thread: Rasterizer, Surface
    * IO Thread: IOManager

This patch was reviewed in smaller chunks in the following pull
requests. All comments from the pulls requests has been incorporated
into this patch:

* flutter/assets: https://github.com/flutter/engine/pull/4829
* flutter/common: https://github.com/flutter/engine/pull/4830
* flutter/content_handler: https://github.com/flutter/engine/pull/4831
* flutter/flow: https://github.com/flutter/engine/pull/4832
* flutter/fml: https://github.com/flutter/engine/pull/4833
* flutter/lib/snapshot: https://github.com/flutter/engine/pull/4834
* flutter/lib/ui: https://github.com/flutter/engine/pull/4835
* flutter/runtime: https://github.com/flutter/engine/pull/4836
* flutter/shell: https://github.com/flutter/engine/pull/4837
* flutter/synchronization: https://github.com/flutter/engine/pull/4838
* flutter/testing: https://github.com/flutter/engine/pull/4839

Move generated entry points JSON out of flutter_patched_sdk, add an option to pass entry points to frontend_server (#4734)

Flutter downloads only one version of flutter_patched_sdk, which was obtained from host_debug build on Linux. Generated entry points JSON files are different in profile and release builds (as release build omits observatory), so these files should be downloaded independently of flutter_patched_sdk.

This PR moves generated entry points JSON files from flutter_patched_sdk to a separate directory (out/*/dart_entry_points) and adds an option to specify entry points to frontend_server (as Flutter tools will need to pass custom locations of entry points files outside of flutter_patched_sdk).

* Generate Flutter-specific entry points JSON file while building engine.
* Add ''--tfa' option to front-end server.
* Rename _entryPoint field in front-end server to _mainSource to avoid disambiguation.

* Fixes to make https://dart-review.googlesource.com/c/sdk/+/36641 work with Flutter

* Roll dart

* Update license

* Roll dart

* Update license

* Add libraries.json to dependencies

Add support for --strong option in the engine, create a strong mode version of the platform file (#4504)

* Add a --strong option to the front end server so we can use strong mode with preview-dart-2.

* Plumb the --strong option through the dart controller into the VM.

* - Build a strong version of platform.dill for use with the engine.
- Fix a strong mode static error in the assert statement

* Enable asserts when running debug version even in strong mode.

* Use the correct platform dill file for linking when doing the aot builds.

* Fix formatting issue.

This reverts commit 4caa68b8.

This is for Fuchsia where we would like it to be located at //third_party/flutter.

This reverts commit 83224fb6.

* Change kernel platform generation dependency name

* Include vmservice which is needed by gen_snapshot for Flutter release build

Revert "Revert "Roll dart to pick up change where platform.dill was removed (#4180)" (#4185)" (#4186)

This reverts commit a89f4669.

Doing the synchronized roll of Dart into engine as well as into Fuchsia
to prevent Fuchsia breakage.

This reverts commit 37f571ee.

* Roll dart to pick up change where platform.dill was removed

* Fix flutter patch sdk generation

* Update license hash. No changes to license text.

* Roll dart to pick up a fix for zero-rebuild problem

* Update license hash

These libraries are in Topaz now.

Now it references dart:zircon and dart:fuchsia.

This repository contains FTL now in the Fuchsia build.