Stop using RenderNodeAnimator callbacks

Bug: 17281017

- RenderNodeAnimator's callbacks are asynchronous and thus cannot be
  relied upon for synchronus state changes. Instead use Animator#end()
  and rely on the ValueAnimator synchronously invoking the listener's
  onAnimationStart callback.
- Also to prevent future NPEs, remove mCurrentButton ivar and instead
  specify the source button directly.

Change-Id: I4ca05b46c582474a6ca7e00d8d16df118ede7eb4
1 file changed