While starting to fix the underlying issues of internal PR 174365 (assertion through clearWindow() call when we don't have any target buffer), I realized that this function call is actually entirely unnecessary. That doesn't obviate the need for a proper fix, but why not get rid of it when we have the chance. Patch below, more detailed explanation in the commit message.
Created attachment 152820 [details]
Comment on attachment 152820 [details]
Clearing flags on attachment: 152820
Committed r122876: <http://trac.webkit.org/changeset/122876>
All reviewed patches have been landed. Closing bug.