This is caused by a syscall sandbox violation.
rdar://problem/50931110
Created attachment 370259 [details] Patch
Comment on attachment 370259 [details] Patch r=me.
Comment on attachment 370259 [details] Patch Thanks for reviewing!
Comment on attachment 370259 [details] Patch Clearing flags on attachment: 370259 Committed r245533: <https://trac.webkit.org/changeset/245533>
All reviewed patches have been landed. Closing bug.