Place a black layer behind SurfaceView.

For SurfaceView's which do not implement
SurfaceRedrawNeeded we can see holes through to the
background in various scenarios. We prevent this by
placing a DimLayer behind opaque SurfaceViews. SurfaceFlinger
will remove it from the visible layers when the SurfaceView
totally obscures it.

Bug: 28763785
Change-Id: I9b4d1ba8be786f30432a6a3b42e5616662cdc090