Don't show notifications above FLAG_SHOW_WHEN_LOCKED windows.

We need to hide the bouncer when the lockscreen is occluded
by a show-when-locked window, but we also need to double-check
any time the screen comes on in case the bouncer has been
shown for some other reason since the occlusion originally 
happened.

Bug: 14294001
Change-Id: Ief4ea8e39322d9c4b26ec217dbc14b6c6f16ad45