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This changes the way that SurfaceFlinger's shadow buffer management
works such that instead of tracking the size of the shadow queue in the
BufferQueue, SF tracks the last frame number it has seen, and passes
that into the acquireBuffer call. BufferQueueConsumer then ensures that
it never returns a buffer newer than that frame number, even if that
means that it must return PRESENT_LATER for an otherwise valid buffer.

Change-Id: I3fcb45f683ed660c3f18a8b85ae1f8a962ba6f0e