For some reason the backend changes for https://bugs.webkit.org/show_bug.cgi?id=147230 did not get committed and, as such, it does not work.
Created attachment 258638 [details] Patch
Comment on attachment 258638 [details] Patch Clearing flags on attachment: 258638 Committed r188222: <http://trac.webkit.org/changeset/188222>
All reviewed patches have been landed. Closing bug.