This helper makes it easier to write correct tests that involve
gestures.

Fixes #1855

The example in the spec with multiple actions is an anti-example.

Fixes #1876

We weren't listening to the onChange handler.

Fixes #1850

This makes it match the material spec more.
https://www.google.com/design/spec/style/icons.html

Fixes https://github.com/flutter/flutter/issues/1357

rename example apk dirs to android
removed all BUILD.gn files

(see https://github.com/flutter/flutter/issues/1586)

Each layer is supposed to reexport the parts of the previous layer
that are part of its API.

- In painting.dart, export from dart:ui all the Canvas-related APIs
  that make sense to be used at higher levels, e.g. PaintingStyle.

- Delete painting/shadows.dart. It was dead code.

- In rendering/object.dart, export all of painting.dart.

- In widgets/basic.dart, export all of painting.dart and
  animation.dart. Some classes in animation/ are renamed to make this
  less disruptive and confusing to the namespace.

- Split out Stocks back into an import model rather than a part model,
  so that it's easier to manage its dependencies on a per-file basis.

- Move Ticker to scheduler library.

- Remove as many redundant imports as possible now.

- Some minor nit picking cleanup in various files.

Properly support labels, hints, icons, and custom typography.

Now you can colorize an Icon simply by proving a Color for the Icon.

Instead, require the developer to opt-in to autofocusing because autofocusing
can be disruptive.

Fixes #1307

Introduces a new Tooltip class.
Adds support for tooltips to IconButton and Scaffold.
Adds some tooltips to various demos.

Also some tweaks to stack.dart that I made before I decided not to go
down a "CustomPositioned" route.

The Firebase server seems to have changed behavior and is not giving us a List
instead of a Map. This patch switches us back to GitHub, which just serves the
same flat files all the time.

Previously we used a positional argument for widgets that had multiple
children. Now we use a named argument that defaults to an empty list.

Fixes #241

- Add an option to enable debugPaintSizeEnabled.
- Add an option to enable the StatisticsOverlay.
- Add support for the StatisticsOverlay in MaterialApp.
- Change the layout behaviour of RenderStatisticsBox:
   - Give it a zero intrinsic width.
   - Give it an accurate intrinsic height that depends on the flags
     set. (Also, move the enum to the rendering/ layer from the
     widgets/ layer to enable this.)
   - Make the box automatically size itself full-width and the correct
     height, so that you can actually embed it (though most of the
     time you'd just put it in a Stack so this doesn't matter as
     much, really).
- Some style nit fixes in statistics_box.dart.

Instead of taking a builder and a generic type, we can just take a
List<Widget>.

This will make it much easier to add more settings.

See https://www.google.com/design/spec/layout/metrics-keylines.html#

This patch moves PageableList off HomogeneousViewport and onto RenderList and
friends, making it match the new ScrollableList.

ScrollableList2 is complete and subsumes all the use cases for the original
ScrollableList.

This patch also changed ScrollableList2 to use an Iterable instead of an
List for its children. This change lets clients map their underlying
data lazily. If the clients actually have a concrete list, we skip the
extra copy and grab the child list directly.

Not great.  Better than nothing.

@hixie

The TabBarSelection change animation needs to start where the fling's drag gesture ended rather than from zero.  The intial vlaue of progress for the TabBarSelection's performance is now converted from the range used during an interactive drag, to the range used when animating from the previously selected tab to the new one.

TabBarSelection now requires a maxIndex parameter.

This matches the naming pattern expected from package:test
`flutter test` doesn't care, since it finds all _test.dart
files and runs them regardless of directory.

@Hixie

I had to add a setLocale method to WidgetTester and
split the code in FlutterBinding which handled locale
changes to allow me to dispatch a locale change w/o actually
changing what the c++ code reports as the locale.

Also added the test to Travis.

@abarth @jason-simmons