base

Synchronize recents to freeform transition.

Recents to freeform animation must hang on the first frame and inform
Recents to hide its views. This mirrors the transition from freeform
to Recents, where the animation needs to hang on the last frame.

We need a special window flag for recents to force a redraw after the
animation launches. At this point Recents will become not visible
from the perspective of the activity manager, which would prevent
further drawing. We make recents ignore that and instead depend on
window visibility which will change after recents exit animation
finishes.

Bug: 24913782
Change-Id: Ief743b7e6fcebb3d8789d4745fb122ac607c1cf0