De-jank quick contact animation

Bug:6508325
Bug:6501917

This change ensures the layer allocation does not happen during the animation.
This change also modifies the way the background fade is implemented to
make it faster (halves the required fillrate, which is necessary given we
are falling back to GPU composition in this particular case.)

Change-Id: I27023ad1a5af06d2d2036baed24c2f47deb85184