Apply https://chromium-review.googlesource.com/c/chromium/src/+/646640 on ToT.

Optional: --disable-checker-imaging

Open mobile.twitter.com, log in and scroll the page. A lot of tiles will flicker.

Moving the pending gpu work tiles processing from the task set callbacks to CheckAndIssueSignals fixes the problem.

I think this is a fundamental problem with async gpu raster. We want to delay activation until required for activation tiles are done on the gpu service. However, if the (activated) pending tree scrolls after activation, the new tiles may not have completed on the gpu and marked as ready to draw.