http/tests/misc/detach-during-notifyDone.html has been crashing flakily, probably since it was added in r192844. First recorded crash is r192874, but I think that's just due to test bot downtime.
The test(s) filed under this bug have been consistently passing for the last 4000 revisions. Marking bug as fixed. Committed r263254: <https://trac.webkit.org/changeset/263254>