Created attachment 396443 [details]
Element backgrounds fail to paint sometimes when scrolling in gmail with async overflow scrolling enabled.
I think this is about painting with stale clip rects (which are probably computed using some stale main-thread scrolling offset).
We paint out-of-view tiles but RenderBlock::paint() short-circuits because they are clipped out (note the iOS #ifdef), then we later scroll those tiles back into view and they are missing content.
RenderBox::overflowRectForPaintRejection() is supposed to handle this, but m_overflow is null for some reason.
Created attachment 396478 [details]
Created attachment 396494 [details]