We currently tile the area outside the visible rect, in circles (or rather stars) from the inside-out. On pages which are blocking, this looks quite bad while scrolling, so the idea is to tile in rects instead.
Created attachment 128987 [details] Patch
Comment on attachment 128987 [details] Patch Wrong patch!
Created attachment 129014 [details] Patch
Comment on attachment 129014 [details] Patch Makes sense if we use the trajectory vector to discard tiles outside the viewport when panning. LGTM.
Created attachment 129022 [details] Patch
Comment on attachment 129022 [details] Patch Clearing flags on attachment: 129022 Committed r109112: <http://trac.webkit.org/changeset/109112>
All reviewed patches have been landed. Closing bug.