* Implements FlatButton debugFillDescription

* Fix doc comment

* Override debugFillProperties instead of debugFillDescription

* Remove child debug property

* Add capability to print engine dart sdk to flutter doctor

* First round of review comments

* second round of comments

* Final review comments

* Fixed typo in navigator.dart doc comments

* Added survey js to docs template

Add support for IOS_SIMULATOR_HOME environment variable in IOSSimulator.logFilePath

flutter_tools can be run on environments where the user's HOME directory
is not the root of the iOS simulators' configs. This change adds support
for such environments by allowing the caller to set the simulator root
directory via an environment variable.

In https://github.com/flutter/flutter/pull/13141 I updated the demo name
from 'Animated Images' to 'Animated images' before submitted, but did
not update the name in the smoketest and transitions_perf test.

Existing microbenchmarks task is extended instead of adding a new one to consume less horizontal space on Flutter dashboard.

This fills out the following matrix:

App: `flutter create` default app, Complex Layout, and Gallery.
Platforms: Linux/Android, Mac/iOS, Windows/Android
Build modes: full release, aot blobs, debug
Dart: normal, 2.0 preview

It also renames all the tests that used "build" to mean compilation
build to use "compile" instead, so that it's much clearer on the
dashboard.

Also, mark some flaky tests that are no longer flaky as not flaky.
Also, remove uses of call() since that's probably going to go away at
some point.

This consolidates all of the non-template .gitignore rules into the top level .gitignore, to ignore common things more broadly, with less maintenance needed for the .gitignore files. Does not touch the templates, so that they still produce needed .gitignores as part of flutter create.

* add an assert to validate the RefreshIndicator.onRefresh result

* add a test for RefreshIndicator.onRefresh assert

* switch to using FlutterError.reportError, FlutterErrorDetails, and FlutterError

This reverts commit e73d4061.

It caused major performance regressions.

This was fixed in #13150.

That commit rolled the engine to:
  flutter/engine@93b21795971357edbfd646f61b8d7f62388b0dae,

which rolled Dart to:
  dart-lang/sdk@70e5deacb54aea295665215837adaedd3d6a5bfa

which includes:
  dart-lang/sdk@d38c08d97358ebe4ee30e557bfee339dddda9b7a

Which fixes the breakage introduced in #13134.

This reverts commit f5d9c777.

This patch reorganises flutter_driver's lib/src directory into three
subdirectories:

* driver: sources transitively imported/exported by flutter_driver.dart,
  which defines the API used by driver tests executed on the host machine.

* extension: sources transitively imported/exported by
  driver_extension.dart, which defines the API used to instrument a
  Flutter app running on the target device for use with a driver test.

* common: sources common to both driver and extension code.

This makes rolling Flutter into repositories that use Bazel (or
Bazel-like build systems) significantly more robust, due to the simpler
glob patterns involved.

This is a bug in my previous CL: instead of cancelling the timer if
there are no more listeners, I canceled it if there were listeners (I
can claim I just missed a not :) ).

Not cancelling the timer when removing the last listener was not that bad, as
the timer callback is guarded by a check to see if there are listeners.
So the animation will not continue.

But in the case there were multiple listeners on the same stream, and
one of them is removed, this bug will stop the animation for all other
listeners.
I added a test case for this scenario.

Fix the dismissible demo in the gallery (make it actuall update when you pick something from its menu; give it a better affordance for resetting once you've dismissed everything).

Improve some docs.

Fix various flinging bugs with dismissible. Add tests for those cases.

Add a feature to flutter_test to support a drag-then-fling gesture (used by the flinging tests).

* feat: add optional headers params to network image

* fix: addressed comments

* feat: add test

* style: format code

* Add missing onDragCompleted to LongPressDraggable

* Add test for LongPressDraggable onDragStarted and onDragCompleted

Changed the ExpansionTile widget to have an optional value to
initialize the widget as collapsed or expanded.

The widget will be collapsed by default.

Use of this file was eliminated in e7657b94.