[tracing] refactor TracingController

- remove the unnecessary MessageLoop
- split stopping the trace from downloading it
- support waiting for the trace file to be finalized
- fix the missing null-termination in the trace data string

If a custom ICU data file path is specified, attempt loading from that instead of loading from the default path.

Handle both absolute and relative paths when generating sky_snapshot …

Remove Picture.playback, and other clarifications

If a custom ICU data file path is specified, attempt loading from that instead of loading from the default path.

Keyboard can get out of sync with flutter

We need to tell the InputMethodManager to restartInput whenever we change our
editing state or else it might persist state from earlier in the editing
session.

Fixes https://github.com/flutter/flutter/issues/2431

Allow PlatformMacMain to be called mutliple times by third party flutter embedders

Depfile support for sky_snaphot.

--build-output.
Also, dependency collection should be done by Loader.

If we control the embedder, we call it just once and have it wrap UIApplicationMain.

Prepare a framework providing an embeddable Flutter view controller

Ref #1942

Hide implementation comment we leaked into docs

Fix ImageShader crash, and add dartdocs

Adds or augments the documentation of various objects in dart:ui.

Removes the ignored argument to SceneBuilder.

Hide the default constructor on Gradient.

Add a call to the ImageShader constructor.

Reorder some members so that private versions come after public versions
so that docs will come before both.

iOS: Export symbols for public API from the framework dylib

Also, add some dartdocs for AppLifecycleState values.

iOS: Cleanup and move guts of the embedder into FlutterViewController.

* Remove engine code from SkySurface into the controller.
* The public API exposed by Flutter.framework for third-party embedders is present ios/public.
* Public view controller API uses idiomatic Objective-C and is subclassable by consumers.
* Paves way for moving the embedder into a framework.

Conditional directives are a snapshotter option. Remove the same from the embedder VM and add the flag to the precomp snapshotter.

Conditional directives are a snapshotter option. Remove the same from the embedder VM and add the flag to the precomp snapshotter.

iOS: Only add the kDartConditionalDirectivesArgs flags when not using precompilation

Wire up locale notifications to ios.

Fixes #2282

update the embedder file

Update the expected argument count in the SceneBuilder constructor

Enable conditional directives

Match fonts based on weight and style attributes

Add more dartdoc to dart:ui