Fix Contacts animation jank

The last frame of an animation stays stuck on the screen for a couple of frames.
Specifically, the "Quick Contact" animation that animates the picture
closed (fades/scales it away) animates all the way to the end... then hangs there
briefly before being taken down.

The problem is a rendering bug where we correctly detect that a DisplayList
has nothing to draw (since the last frame is completely transparent, alpha==0),
but incorrectly ignore the fact that we cleared the transparent-background
window prior to not-drawing that DisplayList. When we detect that there's
nothing to draw, we don't bother swapping buffers. So even though we drew
the right thing (clearing the buffer), we didn't actually post the buffer to the
screen.

This change factors in both the clear and the draw to decide when to swap buffers.

Issue #8564865 Quick contact close animation jank redux

Change-Id: Ib922cff88a94f025b62f7461c1a29e96fe454838