Correct SurfaceView background visibility.

This corrects an error introduced in a recent refactoring. The background
SHOULD be visible when the SurfaceView is opaque, the idea being that the background
will provide for opacity even if the SurfaceView hasn't finished rendering.

Bug: 123421088
Test: Manual. SurfaceViewSyncTests. ASurfaceControlTest.
Change-Id: Ie0690e07474c30d9324e0b0f26db136e4d7a0fa2