This is because the HUD code expected the PlatformCanvas it uses to be cleared on creation which is no longer happening after http://src.chromium.org/viewvc/chrome?view=rev&revision=127196.
Created attachment 133156 [details] Proposed Patch
Comment on attachment 133156 [details] Proposed Patch Thanks for fixing this. :)
Comment on attachment 133156 [details] Proposed Patch Clearing flags on attachment: 133156 Committed r111641: <http://trac.webkit.org/changeset/111641>
All reviewed patches have been landed. Closing bug.