We're already doing this. In any case we should remove the FIXME in the code add add some test coverage.
This involves merging Blink r161876
Created attachment 228737 [details]
Comment on attachment 228737 [details]
Clearing flags on attachment: 228737
Committed r166923: <http://trac.webkit.org/changeset/166923>
All reviewed patches have been landed. Closing bug.