Tests in fast/frames/flattening became very unstable after backing store was introduced for painting in the GTK port (r98827). There are occasions when the tests pass without anomalies, but most often there appear some flaky tests and also tests that fail even on retry. Martin suggests skipping these tests while he's working on polishing the whole thing. Patch incoming.
Created attachment 113684 [details] Patch
Comment on attachment 113684 [details] Patch Clearing flags on attachment: 113684 Committed r99360: <http://trac.webkit.org/changeset/99360>
The issue seems to be that many frame flattening tests wait until the <body onload> event on the body to call layoutTestController.setFrameFlatteningEnabled(true). Toggling the frame flattening setting does not trigger a relayout. If the first layout happens before <body onload> the page will be in the incorrect state. I'm uploading a patch that toggles the setting immediately instead of waiting until onload. This seems to remove the flakiness on my machine.
Created attachment 113769 [details] Patch
Comment on attachment 113769 [details] Patch Clearing flags on attachment: 113769 Committed r99361: <http://trac.webkit.org/changeset/99361>
All reviewed patches have been landed. Closing bug.