Add support for Choreographer animations

First step to add support for Choreographer based animations. The
Choreographer_Delegate avoid using a handler so the animation callbacks
can be called on-demand (by using doFrame). This allows things like
frame by frame animation or selecting a specific frame, and doesn't need
a separate thread to run.

The CL also changes the System and SystemClock implementations to allow
to set specific times. Because animations heavily rely on the system
time, this allows controlling it. It can also be useful to ensure that
the rendering produces a deterministic result when using controls like
the Calendar widget.

Change-Id: Iff221d2698a82075cafbb60f341be01741f7aa13