Animate from Choreographer only.

Animation steps are now executed on a Thread launched from the
Choreographer rather than being called at the end of the WindowManager
layout process. Animations and layout are still tightly coupled in
that they share considerable state information and neither can be
executed without holding a lock on WindowServiceManager.mWindowMap.

Change-Id: Ie17d693706971507b50aa473da1b7258e9e67764