Due to a variety of reasons, layer lists sent to the hwc will include layers that are occluded by fullscreen opaque layers higher in z-order. This often happens with color layers. The extra wait times and memory traffic incurred by this isn't free. A simple heuristic that clears the display list when a fullscreen opaque layer is added to the top should have a positive impact on performance.

Pretty easy win in compositor that should improve perf and/or power usage.