fb: post time-critical systemui flags to window manager

thanks Kiril for this suggestion. We are already using window
manager for other things in immersive mode....so nice addition
to fix a race condition

Change-Id: I5d818214d7864014fa77c0d562d2908110d93303
WindowManagerService: fix application transitions in expanded mode.

Change-Id: If7d3fc3ab566dedc3a5b38cd0a6dc3185f494e20