Chrome Version: ToT
OS: All

To paint the contents of clipping mask layers, we use the full paint machinery including paint offsets, several layers of paint methods in a call hierarchy, layout object queries and more.

All we need to do is fill the area bounded by the clip rects with black.

This will save all those method calls, and a bunch of if checks that slow down every other paint operation, and makes border-radius for composited children much more efficient and less complex.