Expose the window flags for lights out mode.

I hadn't wanted to do this, but it makes porting the FLAG_FULLSCREEN
stuff over to this simpler because you don't have to go find a view
to proxy through.

This change also clears the flag everywhere when the window manager
notifies the views that the change has come back.

Change-Id: I48392c7550925bcca50c5bb9e1f263e99de6c7bc