This is unused by us. It was added for Inspector extensions, which is a feature we don't have.
Created attachment 219492 [details] [PATCH] Proposed Fix
Comment on attachment 219492 [details] [PATCH] Proposed Fix Clearing flags on attachment: 219492 Committed r160751: <http://trac.webkit.org/changeset/160751>
All reviewed patches have been landed. Closing bug.