The comment about compositing on the UI process was added on r109302 <http://trac.webkit.org/r109302> but was not removed properly when the Qt port was removed from trunk.
Created attachment 293694 [details] Patch
Comment on attachment 293694 [details] Patch Clearing flags on attachment: 293694 Committed r208305: <http://trac.webkit.org/changeset/208305>
All reviewed patches have been landed. Closing bug.