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

* Generate and use frontend_server.d to guard against reusing outdated dill files when frontend_server changes.

* Put generated kernel files into <build> directory

* USe default value for kernel file

Pull code out of flx.dart:assemble() to make flx.dart:buildAssets
which creates the AssetBundle. This will allow us to create just
this instead of an entire FLX.

* Make the current command injected into the AppContext, allowing
  other classes to inject the current command.
* Introduce `AssetBundleFactory`, an injected factory class for
  spawning instances of `AssetBundle`. This allows other run contexts
  to use custom asset bundling logic.
* Clean up RunCommand by removing a 'packages' argument that duplicated
  a global argument by the same name (and for the same purpose).
  Duplicate arguments are confusing and error-prone.

Fixes https://github.com/flutter/flutter/issues/14058.

* 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

* Fix handling --preview-dart-2 for ios

* final var

This reverts commit 9534082f.

Causes hot_mode_dev_cycle__preview_dart_2_benchmark test timeout.

* Check frontend_server exit code.

When frontend_server completes abnormally, flutter tools has to stop and let user know.

* Add tests

* Plumb a --strong option through to the front end server and the engine
so that we can run flutter apps in preview-dart-2 and strong mode

* - Address analyzer lint issues
*- correctly set up strong mode option in the case of AOT builds

* Use IKG for restarts, use IKG with ProtectedFileByteStore.

* Fix comment, add end of file newline.

* Remove unused import

This adds --preview-dart-2 flag that enables use of Dart 2.0 Frontend in Flutter tools.

Extract a Snapshotter class that can be shared between FLX snapshotting,
AOT snapshotting, and assembly AOT snapshotting. Allows for better
testability of snapshotting logic.

* Extracts script snapshotting used in FLX build.
* Adds tests for snapshot checksumming, build invalidation/skipping.

Remaining work: disentangle + extract AOT snapshotting and Assembly AOT
snapshotting logic from build_aot.dart.

This change re-introduces skipping AOT snapshot builds if input sources
and outputs have not changed since the last snapshot build, assuming a
build for the same platform in the same build mode.

This reverts commit 3d5afb5a.
It includes the following changes relative to the original:
  1. Include the entrypoint source in the checksums
  2. include the build mode in the checksums
  3. include the target platform in the checksums

This change ensures that snapshot build checksums used to avoid
duplicate builds are invalidated by a change to framework revision
(in case gen_snapshot is updated), as well as by build mode.

Currently, only FLX snapshotting uses checksums to avoid duplicate
builds. FLX snapshotting is always done with BuildMode.debug, so didn't
include build mode in the checksum file.

During FLX snapshotting, changes to (or absence of) any of the following
should trigger re-snapshot:

  1. main() entrypoint source
  2. transitive closure of sources reachable from the entrypoint source
  3. the output snapshot

This reverts commit 1705bf3c.

* Revert "Fix a typo in the saved certificate error message (#11640)"

This reverts commit bfda885a.

* Revert "Rollback patch that broke microbenchmarks (#11616)"

This reverts commit 70fe6f4c.

* Revert "Extract snapshotting logic to Snapshotter class (#11591)"

This reverts commit 309a2d78.

* Revert "Minor whitespace formatting fix (#11590)"

This reverts commit bf69c3c6.

* Revert "Avoid rebuilding snapshots if no change to source (#11551)"

This reverts commit 74835db5.

First step in eliminating code duplication between script snapshotting
(in FLX build) and AOT, assembly AOT snapshotting.

This change re-introduces skipping snapshot builds if input sources (and
outputs) have not changed since the last snapshot build, with a bugfix
to include the entry-point source in the checksum used to check whether
rebuild can be skipped. This ensures that the following sequence
invalidates the cached build, resulting in two snapshot builds:

  flutter build ios lib/foo.dart
  flutter build ios lib/bar.dart

This reverts commit 3d5afb5a.

* Revert "Support space- and backslash-escaped dependencies (#11090)"

This reverts commit e6bafd0b.

* Revert "Skip AOT snapshot build if inputs are unchanged (#11084)"

This reverts commit b5e522e2.

Previously, the snapshot file was recomputed on every build. We now
record checksums for all snapshot inputs (which are catalogued in the
snapshot dependencies file output alongside the snapshot) and only
rebuild if the checksum for any input file (or the previous output file) has
changed.

Previously, the snapshot file was recomputed on every build. We now
record checksums for all snapshot inputs (which are catalogued in the
snapshot dependencies file output alongside the snapshot) and only
rebuild if the checksum for any input file has changed.

* Only one call to createSnapshot exists, and it's in the same library.

* Eliminate conditional logic around the presence of depfilePath, the
  only existing call always passes a non-null depfilePath.

Support for placing an AOT dylib in the flx.  Part of Fuchsia AOT support.

* add @required when there's an assert not null

* address review comments

* Remove legacy .apk build.

Print out an error message telling the user to upgrade the project if
it's not Gradle-based. Removed all the obvious traces of the legacy
build.

Added support for Dart VM kernel snapshots in Gradle builds.

Fixed Android installs to verify that the app is actually installed, and
not just rely on the presence of the .sha1 file.

gen_snapshot is now used for both JIT and AOT snapshots.  The JIT version
used in debug mode will be a 64-bit binary.

* Use snapshot's .d file as source inputs in Gradle build.

If we don't yet have a .d file (first build), fall back to using the
.dart files in the current directory. This enables us to detect changes
in dependent source files (Flutter framework, packages outside the
source directory, etc.), and re-generate the snapshots as needed.

Unfortunately, Gradle requires knowing the source files before executing
the task, and can't update them after building, so Gradle considers the
second build to be out-of-date (because it has more input files than the
first build). Sub-sequent builds have the correct dependency
information, and will be skipped if the source files haven't changed.

Also added a dependency on gen_snapshot. The snapshot ABI isn't stable,
so we need to re-generate the snapshots when we roll the Dart SDK
dependency.

Fixes #8315
Fixes #8687
Fixes #8607

* eliminate sky snapshot

* roll engine

* Enable Hot Reload on Windows (backed by gen_snapshot)

\o/

Two caveats:
* Hot Reload on Windows is slower than on other platforms because gen_snapshot is slower then sky_snapshot
* We currently cannot hot reload projects with spaces in the path

* enable tests