We used to do this in the SkPicture, but it's simpler to do it in the
rasterizer now that we're using multiple SkPictures in Dart.

Separate the notions of offset and size in compositing

Separating these notions makes them easier to work with because offset is
relative to the parent layer whereas size is intrinsic to the layer itself.
This patch fixes the underpainting bugs when compositing the stocks example.

Generalize _cleanRelayoutSubtreeRootChildren into visitChildren

This generalization will let us implement other alogorithims that need to walk
the RenderObject tree.

Remove stray reference to Typeface

Add a ValueAnimation helper class for AnimationPerfomance.

Fix analyzer warnings

Roll back drawText Canvas support; we are instead going to refactor RenderParagraph into ParagraphPainter

Updates to game sound API

Add a compositing step to the lifecycle

Now we have the ability to draw multiple PictureLayers. We still squash all the
pictures together into a single SkPicture for simplicity. In the future, we'll
submit them to C++ separately and composite them on the GPU thread.

Adds CicularProgressIndicator and LinearProgressIndicator

Setting a ProgressIndicator's value to null (the default) makes it an "indeterminate progress" or activity indicator.

The indeterminate animations for both kinds of progress bars are essentially the same and wrong vis the Material Design spec, http://www.google.com/design/spec/components/progress-activity.html. I'll improve conformity with the visual design in a future CL.

Setting a ProgressIndicator's value to null (the default) makes it an "indeterminate progress" or activity indicator.

The indeterminate animations for both kinds of progress bars are essentially the same and wrong vis the Material Design spec, http://www.google.com/design/spec/components/progress-activity.html. I'll improve conformity with the visual design in a future CL.

Expose longpress and showpress in Listener

Removes the ability to jump to different positions in sound effects (this isn't supported on Android)

Fixed a typo in the widget tutorial.

Switch painting over to using PictureLayer

Used for AnimationPerformance with a single AnimatedValue<T> variable.

Currently we have a single PictureLayer that everyone draws into. A future
patch will teach the system to use multiple PictureLayers.

Make |TracingController| platform agnostic and enable collecting traces from base and the shell view dart isolate simultaneously

Adds sounds to demo game bundle

Adds rough sound support for sprites

traces from base and the shell view dart isolate simultaneously.
Trace files contain samples from multiple sources and must be merged
separately

Rename createsNewDisplayList to requiresCompositing

This patch prepares for introducing the compositing system by repurposing the
relevant parts of the createsNewDisplayList system. This patch also removes the
no-longer-relevant parts of that system.

Don't claim to be a text editor

http://developer.android.com/reference/android/view/View.html#onCheckIsTextEditor()
says that we should return true if the "primary purpose" of
the view is text editing.  The keyboard still seems to work
fine if we return false here (default implementation) so
I'm removing this for now.

Fixes https://github.com/domokit/sky_engine/issues/116

@abarth