The problem was a black first frame when creating a surface, or a
garbage frame when the surface was resized.
The cause was lack of synchronization between the render thread and the
UI thread. The UI thread would typically return before the render thread
had a chance to draw its first frame.
The fix was to make the UI thread wait until at least one frame had been
rendered by the rendering thread.
The waiting is done in the surfaceChanged method because we know
that surfaceChanged will be called in both the surface created
and surface changed cases.
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