When a window is first shown only draw once while animating.

On some hardware allocating a new graphics buffer is quite
expensive, which blocks updates to the UI.  This can cause
glitches when performing window animations.

To reduce these glitches, the view hierarchy will now only
allow itself to be drawn once if its window is being shown
while the window manager is animating, not resuming draws
until it is told that the animation is done.

Change-Id: Ie15192f6fddbd0931b022a72c76ddd55ca266d84