Reduce jank in QuickContactActivity dismissal.

Wait for final frame of dismissal animation to be drawn before
calling Activity.finish().  Also, handle the background transition
ourselves instead of using the "backgroundDimEnabled" property;
this saves us one extra overdraw on the entire screen.

Bug: 6209669
Change-Id: Ie1e295755185f15b5d5326050cbd990563860a6f