We've always cached kernel compiles during bundle builds. This adds
caching for kernel compiles during AOT builds by moving caching into the
KernelCompiler.compile() method rather than around each invocation of it.

This also filters buildbot paths included by the kernel compile that are
not present on the local machine at paths /b/build/slave/Linux_Engine/...
The kernel compiler should probably include an option to not emit these
paths in the depfile, since these are used both by Gradle and the
Fingerprinter class.

CompilerOutput values should never be mutated. Also includes minor
formatting change to the compile() method signature in line with the
style guide.

Minor housekeeping while I'm touching other bits of nearby code.

Wraps the compile function in a class injected via the global context,
which makes it easier to mock in unit tests -- specifically tests for
AOT snapshotting, which already require pretty significant amounts of
mock inputs.

This reverts commit b0b2c007.

* Turn support for sync-async on in Flutter. With this feature
execution of async functions starts immediately instead of it
being delayed by one microtask tick.

* Address review comments.

* Adjust some stack trace expectations which are slightly different with
--sync-async turned on.

* Handle error count reported by frontend.

Extend compilation result from single string to a structure(string filename and integer error count).

* Use ?.

* Include engine roll with dart sdk roll.

* parse(onError) -> tryParse

* Make '?? throw' more readable and avoid issue with analyzer

* Fix test so it mocks compiler output including errors count

Fixes https://github.com/flutter/flutter/issues/15361

* Use uris for hot reload invalidation.

* Clean up unneccessary conversions

* add final.

* Revert sample change

* Revert "Revert "Reland pass filesystem options (#15622)" (#15651)"

This reverts commit 0f3eada0.

* Fix for windows failing test

* !isEmpty -> isNotEmpty

This reverts commit bbcf55a5 as it breaks hot reload on Windows.

* Revert "Revert "Pass filesystem-root, filesystem-scheme options through `flutter run, build` and gradle. (#15592)" (#15621)"

This reverts commit c663e336.

* Check whether filesystem-root is emtpy.

* Restore broken merge

* Fix windows test

* Adjust regex in test. Invalidate files by file path.

Revert "Pass filesystem-root, filesystem-scheme options through `flutter run, build` and gradle. (#15592)" (#15621)

This reverts commit 0f659fb1 as it
breaks bin/tasks/gradle_plugin_test.dart.

* Pass filesystem-root, filesystem-scheme options through flutter run/build/gradle.

* Pass entry points JSON files to front-end server (#15180)

* Fix ios/debug build which uses 'flutter build aot': do not require entry points files and disable AOT transformations in this mode

* Revert "Pass entry points JSON files to front-end server (#15180)"

This reverts commit 0edea887.

Reason: buildbot failures on Mac.

* Add to Artifacts, and add optional arguments to entry points for flut… (#15185)

Add to Artifacts, and add optional arguments to entry points for flutter run and test to allow for wiring up the same with preview-dart-2 internally

* Changing packages uri here is not necessary

This reverts commit e0f6e626.

Add to Artifacts, and add optional arguments to entry points for flutter run and test to allow for wiring up the same with preview-dart-2 internally

* Use depfile in --preview-dart-2 mode.

* Generate and use frontend_server.d to guard against reusing outdated dill files when frontend_server changes.

Changes since last roll:
  - Leave only widget creation tracker kernel pass in flutter frontend server. (#4727).

* Run flutter tests in preview-dart-2 mode on travis flutter builds.

* Run dart2 tests on osx. Run dart tests in dart2.

* Fix name camelCase

* Default options to empty array, rather than null

* Troubleshoot failures

* More logging

* Troubleshoot: run single test

* Troubleshoot: run 15 tests

* Troubleshoot: run 15 tests with fix

* Try limit concurrency to 1

* Limit concurrency for preview-dart-2 tests to 4

* Move dart2 tests to allow_failures section

* Reinstate tests_dart_2 shard

* Raise concurrency to 8

* Reuse compiler across multiple test runs

* Allow to switch entry points when recompiling.

Actually use single compiler to incrementally recompile all tests executed by 'flutter test'.

* Remove leftover commented code

* Fix comment

* Lints

This is needed to support running with local engine's dart sdk.

This is follow-up to https://github.com/flutter/flutter/pull/14702.

* Use already downloaded dart sdk for frontend_server.

This is follow-up to https://github.com/flutter/flutter/pull/14610

* Remove reference to engine dart-sdk from artifacts

* Remove unused imports

* WIP to switch back to solution where dart sdk is downloaded into bin/cache/dart-sdk, but it is 'flutter precache -a' that can download all dart sdks for other platforms under bin/cache/artifacts/engine/<platform>/dart-sdk

* Download all dart sdks when 'flutter precache -a'

* Put generated kernel files into <build> directory

* USe default value for kernel file

* Reland 9534082f with fix for incremental compilation.

When in incremental mode, awaiting exitCode won't work because compiler is not expected to exit after compilation.
Instead listen for stdout stream closing and report error if outputFilename has not been received.

* Fix lints

This reverts commit 9534082f.

Causes hot_mode_dev_cycle__preview_dart_2_benchmark test timeout.