JIRA 452460 So what happens here is that when the screen goes dark, all tiles are freed up to release memory back to the system. We also mark the contents as dirty. However, we still remember that we've rendered e.g. tiles 0,0 and 0,1 in the past because those were visible at one time. This is part of an optimization to avoid re-rendering tiles repeatedly until the UI thread catches up with the fact that we have indeed rendered those tiles (which will happen when the UI thread next composites a frame). When contents are dirty, we're not supposed to perform this optimization (skip rendering) because the appearance of the layer has changed, so we do need to render those tiles. Unfortunately, the code that's supposed to forget the list of tiles rendered is in a conditional, "if (frontVisibility)", which happens to be false when the screen comes on again. So we end up perpetually skipping those render jobs at 0,0 and 0,1, and the UI thread keeps yelling at us to render them.
Created attachment 207526 [details] Patch
Comment on attachment 207526 [details] Patch Clearing flags on attachment: 207526 Committed r153372: <http://trac.webkit.org/changeset/153372>
All reviewed patches have been landed. Closing bug.