For <https://bugs.webkit.org/show_bug.cgi?id=174751>, it's not known what users are doing to trigger this crash, but we can at least come up with a unit test for it given what we know (see r219765's ChangeLog for more details).
Created attachment 316308 [details] Patch
Created attachment 316309 [details] Don't include more SPI than is needed.
Comment on attachment 316309 [details] Don't include more SPI than is needed. Clearing flags on attachment: 316309 Committed r219836: <http://trac.webkit.org/changeset/219836>
All reviewed patches have been landed. Closing bug.