Make surface management between SurfaceView and the window manager
much more controlled, to ensure that SurfaceView always gets to report
the current surface is destroyed before the window manager actually
destroys it.
Also a small tweak to allow windows that have a wallpaper background
to still have a preview window. This makes launching home after it
has been killed feel much more responsive.
Change-Id: I0d22cf178a499601a770cb1dbadef7487e392d85
6d05fd3c79