Reinstate SurfaceView Background from N

In N we used a Dim-Layer to add a background to SurfaceView, from
the WM side. In O we forgot to reimplment this with the new SurfaceView
and so we once again can have holes for apps which don't implement
surfaceRedrawNeeded.

Bug: 62113351
Test: Manual from bug. go/wm-smoke
Change-Id: If3dac51886b9a8083140da7b5bc1b349da57860f