The override object is using a compositing thread WebOverlayPrivate object with no client because the layer doesn't delegate drawing to the WebOverlayPrivate, it's only used to modify the override properties on the underlying compositing thread layer.
Created attachment 145077 [details] Patch
Comment on attachment 145077 [details] Patch Looks good.
Comment on attachment 145077 [details] Patch Clearing flags on attachment: 145077 Committed r119126: <http://trac.webkit.org/changeset/119126>
All reviewed patches have been landed. Closing bug.