* Introduce frontend_server that allows for interactive and batch modes.

Example of batch mode:
```
$ dart $HOME/p/f/t11/flutter/engine/src/flutter/frontend_server/bin/server.dart --sdk-root=$HOME/p/f/t11/flutter/engine/src/out/android_debug/flutter_patched_sdk --platform-kernel-dill=$HOME/p/f/t11/flutter/engine/src/out/android_debug/flutter_patched_sdk/platform.dill $HOME/p/f/t11/flutter/flutter/examples/flutter_gallery/lib/main.dart

out: result 79256789-598c-4909-a9e4-0ef36d4c26ba
out: 'State&TickerProviderStateMixin^#U0^' is exported from both 'package:flutter/src/widgets/animated_cross_fade.dart' and 'package:flutter/src/widgets/animated_list.dart'.
...
out: Superclass has no method named 'hitTest'.
out: 79256789-598c-4909-a9e4-0ef36d4c26ba $HOME/p/f/t11/flutter/flutter/examples/flutter_gallery/lib/main.dart.dill
$
```

Example of interactive mode - communication via stdin/stdout:
```
$ dart $HOME/p/f/t11/flutter/engine/src/flutter/frontend_server/bin/server.dart --sdk-root=$HOME/p/f/t11/flutter/engine/src/out/android_debug/flutter_patched_sdk --platform-kernel-dill=$HOME/p/f/t11/flutter/engine/src/out/android_debug/flutter_patched_sdk/platform.dill --incremental

out: Frontend server is ready.
in: compile abc.dart
out: result fd99c0f9-12bb-4083-818e-2521d454fdc8
out: fd99c0f9-12bb-4083-818e-2521d454fdc8 abc.dart.dill
in: accept
in: recompile kuka
in: 123.dart
in: 456.dart
in: kuka
out: result d12f8d05-6c79-44f7-a775-1d3469e1be53
in: quit
$
```

* Add test. Cleanup dependencies.

* One more test with mocks

* Remove platform-kernel option. Refactored CompilerOptions. Clean up comments.

* Update license

* Use Uri.base.resolve consistently. Ensure folder path for sdk root. Fix test.

* Fix main_dart for frontend_server build target

* Reintroduce .packages file, add README.md, revert changes to licenses_flutter

* Run analyzer on frontend-server. Update .packages deps so tests can be run too.

* Add analyzer options file

* Clean up dependencies

* Add frontend_server files to license file back

* Fix comment in analysis_options.yaml

* Run frontend_server tests in travis

* Update licenses

* Change a+x permission on travis/test.sh

* pub get before pub run test

* Fix path to when

* Clarify accept/reject instructions

* Formatting, fixed docs, style

* Update license script to skip .travis.yml, when/example. Update license file.

* Update style nits

* Fix license

* Trim license extracted text. Fix licenses

* Update licenses_third_party signature

* Few more tests

* Update dart license

* Update dart license

* Style changes. Fix return value for Future<Null>

For consistency with Android, when the engine receives a
TextInput.setEditingState message from the framework, and the text has
changed, we now send a TextInputClient.updateEditingState message back
to the framework with the updated state from the engine. The framework
currently relies on this behaviour to trigger onChanged events in
certain scenarios (e.g., on tapping Paste in the selection controls).

Note: it may be more desirable for the framework to trigger the
onChanged calls without relying on the return message from the engine,
but this change ensures consistent behaviour across iOS and Android
until we've evaluated the pros/cons of such an approach.

- Roll Dart to e673ff0b253d8cadd3249aa0d8efe0516606d704
- Update licenses_dart

Also regenerate sky_engine/LICENSE to include libtxt

Fixes https://github.com/flutter/flutter/issues/11586

- Roll Dart to 491390eeaa7974f44a8931d10a899c39c0df8dda
- Register the EmbedderInformationCallback

Use $shlib_toolchain to find the shared_library output file.

If GPURasterizer::NotifyNextFrameOnce was rapidly invoked twice could
have lead to a null pointer exception.

Also ftp::WeakPtr are not thread safe and should not be dereferenced
from other threads.

Create platform API for first frame callback. Use for defer hiding splash screens on Android and iOS (#3956)

* Add back launch screen view until first frame on iOS

* improvements

* Move callback plumbing from ios surfaces to the gpu rasterizer. Didn’t wire java JNI yet.

* Android JNI

* Fix ios reference count and let android engine manage a view on top with launch screen

* Hook up Android activity and view

* review notes

* review notes

* Move thread switching upstream. Use weak references for callbacks.

* Some clean up

The bitmap used to hold a prerolled image in the raster cache must have an
integer width/height in pixels.  However, the picture used to draw the image
may have a non-integer width/height in physical coordinates and thus not
completely fill the bitmap.  The compositor should only select the subset
of the bitmap that reflects the portion filled by the rendered picture.

Without this, the cull rect calculated by an SkPicture may be truncated
to integer pixel coordinates.  The raster cache relies on a precise cull
rect in logical coordinates.

See https://bugs.chromium.org/p/skia/issues/detail?id=6954

* Revert "Revert "Build standalone dart sdk as part of Flutter engine. (#3954)" (#3970)"

This reverts commit 86e007d9.

* Add 7-zip download as a hook

* Advance buildroot dependency

* Fix buildroot dependency

This reverts commit a5bac1ee.

This doesn't work on Windows.

* Update dart deps and add create_sdk for host builds

* Set and use is_flutter flag

* Update to make it compatible with latest changes in https://codereview.chromium.org/2998503002/

* Fix deps

* Roll dart dependency to pick up new arguments

* Merge

* Update deps

* Update license

* roll Dart to 21eddc429e9c7260de00a9af7cad94baba830f59

* update licenses

Roll Dart to 69817eea182384b40ef658d578fd49cac00c5874