This version of the Dynamic Toolbar moves the animation of the toolbar
from the Android UI thread to the compositor thread. All animation for
showing and hiding the toolbar are done with the compositor and a static
snapshot of the real toolbar.
MozReview-Commit-ID: BCe8zpbkWQt
Add AndroidCompositorWidget to act as the intermediary between gfx code
and GeckoLayerClient, in place of AndroidBridge. AndroidCompositorWidget
currently inherits from InProcessCompositorWidget, but when Android
eventually supports OOP compositing, it will be made to inherit from
CompositorWidget directly.
