I'm going to investigate locally, but let's runtime disable it for now.
Created attachment 323482 [details] patch
Comment on attachment 323482 [details] patch r=me
Comment on attachment 323482 [details] patch Clearing flags on attachment: 323482 Committed r223222: <https://trac.webkit.org/changeset/223222>
All reviewed patches have been landed. Closing bug.
<rdar://problem/34946609>