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This mechanism pulls some clip-reduction logic from Impeller Entities up into DisplayListBuilder to simplify the work that Impeller has to do and also amortize the work if the DisplayList is reused from frame to frame. Since the DisplayList does not have access to information such as surface sizes, there will still be cases that Impeller can catch that must be conservatively included by the recording process in the Builder, so this mechanism does not replace the same code in Impeller, it merely catches some cases earlier, while recording widget output, to avoid the same work on every frame down in Impeller. In this first pass only the most conservative and straightforward cases are handled - a clip on a layer which has a previous clip that the new clip fully contains (and which was not already restored). This limited approach is already enough to eliminate a couple of clip operations in the layout of many of the pages in the `new_gallery` benchmarks.