Overlay scrollbars without layers never paint in overflow regions in tiled drawing mode.
Created attachment 141295 [details]
Comment on attachment 141295 [details]
Can we land a regression test for this? Manual test if necessary?
We don't have a way to test overlay scrollbars, and we also don't have a way to test tiled drawing. Even the very simplest <div style="overflow:scroll"> will demonstrate the bug (so long as there is enough overflow to require the scrollbar). I definitely could land a manual test like that, but it's so simple that I'm not sure it's valuable. Is it?