Fixes https://github.com/flutter/flutter/issues/5462

@mpcomplete

Fixes https://github.com/flutter/flutter/issues/5468

Currently, we just treat Fuchsia as TargetPlatform.android, but we might
want to do something more sophisticated in the future.

These tests should hit some previously untested lines.

This commit changes MergeableMaterial to include a flag that
specifies whether connected Material slices should have dividers
between them.

This will ensure cleanup of any files that existed in previous versions of
the artifacts but have since been removed

* use transparent android launcher icons

* revert stocks icons

* Build sky_engine Dart SDK summary bundle on FlutterEngine.download().

* Tweaks for Devon comments.

* Tweaks for Phil comments.

Turns out that previously we weren't updating the clip if the layout
didn't change, even if the delegate was different.

I accidentally checked in this as true in my patch improving this feature.

* new launcher icons for android

* two more sizes for android launcher icons

We have so many render objects going on these days that showing every
box that gets an event just makes the screen blue. This limits it down
to only the ones that are actually doing something with the events.

Also update the AOT builder for changes to the layout of the sky_engine package

* fix an issue where --hot would not exit

* add type annotations

* update the cache earlier

* add documentation

installed changed to installs:
The `flutter run --release` command both builds and installed the Flutter app.
changed to 
The `flutter run --release` command both builds and installs the Flutter app.

Some tweaks to the logo widget:

* remove bad assert
* allow text color to be configured
* make logo pretty in dark mode in gallery
* fix some docs

* Removed unnecessary Shrine hero logic

Instead of a PNG, the Flutter gallery widget is now drawn in code.

There's now a FlutterLogoDecoration class that paints the flutter logo
anywhere you can use a Decoration (e.g. AnimatedContainer).

There's now a FlutterLogo class that honors the IconTheme.

The About dialog box API now takes a Widget for the applicationIcon,
instead of an ImageProvider. It uses IconTheme to make the icon the
right size instead of using an Image widget.

Add padding, duration, and curve properties to the DrawerHeader.
Make the child of a DrawerHeader optional.

Clean up UserAccuntsDrawerHeader a bit.

Add some useful properties and methods to EdgeInsets.

Add some debug logic to RenderDecoratedBox to catch unpaired
save/restore calls when possible.

Make GestureDetector fill its parent if it has no children. Fixes
https://github.com/flutter/flutter/issues/5380

Fixes https://github.com/flutter/flutter/issues/5380

Because parent structure changes when slices gets separated and
merged, children widgets can be rebuilt redundantly. This commit
adds a global key to each child so that the framework always knows
its children apart.

Fixes: https://github.com/flutter/flutter/issues/5336