PIP: Prevent PipOverlayActivity from restarting

PipManager moves the PIPed activity to fullscreen if the activity is
restarted. It's because the activity may be started by the Launcher or
an intent again, but we don't want do so for the PipOverlayActivity.

Bug: 27689029
Change-Id: Icebc09e22e5f5f4650fcdbfdd8c452b7cf23844b
2 files changed