In a mus+ash context, we regress performance by separating Ash and Chrome because their respective Layer Compositor instances have less global layer knowledge and cannot cull as many occluded layers/tiles. We can recover some of this performance by adding quad draw occlusion to the SurfaceAggregator in the DisplayCompositor.

Implementation suggestion: use OcclusionTracker as a guide but adjust for being renderpasses/quads with occlusion computed in each render pass instead of OcclusionTracker's existing layer tree approach.