To avoid rendering artifacts when blitting on scroll in the UIProcess we need to use the FAST_MOBILE_SCROLLING to disable background-attachment: fixed.
Created attachment 133220 [details] Patch
Comment on attachment 133220 [details] Patch Clearing flags on attachment: 133220 Committed r111679: <http://trac.webkit.org/changeset/111679>
All reviewed patches have been landed. Closing bug.