Prevent recents from closing while moving PiP to fullscreen.

If we close recents when beginning the animation, we will
trigger a resume of the previous fullscreen app, which will
attempt to aniamte in at the same time we are animating
the PiP to fullscreen. These conflict causing flicker and
churn.

Bug: 27793381
Change-Id: I520181dadab938bbf62b25891f5ba0e4e9783967