Re-introduce assertion removed in r234890
Created attachment 347193 [details] Patch
Comment on attachment 347193 [details] Patch r=me
Comment on attachment 347193 [details] Patch Clearing flags on attachment: 347193 Committed r234943: <https://trac.webkit.org/changeset/234943>
All reviewed patches have been landed. Closing bug.
<rdar://problem/43389638>