We don't use ui.view anymore.

Icon should use an enum rather than an int for size

Remove unused material edge definition

Material design icons are defined to work at specific sizes: 18, 24, 36, 48.
The current API doesn't reflect that and just takes a size int. If an invalid
size is chosen an error is printed to the console and no icon shows up.

Fixes #1816

Switch clients from ui.view to ui.window

The one we actually use is in material.dart.

Re-host View on Window

After this patch View is just a shim on top of Window and can be removed
easily.

Start booting up the new binding system for window

Default to a known code signing identity when a new XCode project harness is generated

Currently this code isn't completely wired up, but this patch is an incremental
step in that direction.

In the precompiler, add an explicit dependency to the target that generates `dart_ui.dart`

Update Dart revision to pull in armv7 precompiled snapshotting updates

Remove `ios_active_arch` and directly specify `arm64` vs `armv7` preference via `target_cpu`

#1834 Reset tap state after successful tap

Fix a memory leak in CanvasImageDecoder

CanvasImageDecoder is instantiated with a callback into a Dart closure.
That closure was holding references to the ImageDecoder and the returned
Image.  The circular reference between the ImageDecoder and the callback
prevented the objects from being GCed, resulting in leakage of the image
buffer.

CanvasImageDecoder will now destroy the callback after it is invoked,
thus releasing its handle to the Dart closure.

Adds modal bottom sheets: showModalBottomSheet()

Notification of metrics changes.

The Rendering layer binding now multiplexes the dart:ui metrics change
notification so that multiple consumers can all listen to the change.

Add the position at which drags start

Fixes #1807

Add a position to the onTap callback

Fixes #1807

Improves physics debug drawing

Track scroll position

- Change RouteArguments to pass the route's BuildContext rather than
  the Navigator. This caused the bulk of the examples/ and .../test/
  changes (those are mostly mechanical changes). It also meant I could
  simplify Navigator.of().

- Make initState() actually get called when the State's Element is in
  the tree, so you can use Foo.of() functions there. Added a test for
  this also.

- Provide a RouteWidget so that routes have a position in the Widget
  tree. The bulk of the route logic is still in a longer-lived Route
  object for now.

- Make Route.setState() only rebuild the actual route, not the whole
  navigator.

- Provided a Route.of().

- Provided a Route.writeState / Route.readState API that tries to
  identify the clients by their runtimeType, their key, and their
  ancestors keys, up to the nearest ancestor with a GlobalKey.

- Made scrollables hook into this API to track state. Added a test to
  make sure this works.

- Fix the debug output of GestureDetector and the hashCode of
  MixedViewport.

- Fixed ScrollableWidgetListState<T> to handle infinite lists.