KeepAlive fetch should not be blocked in pagehide event handlers
<rdar://problem/65564772>
Created attachment 404906 [details] Patch
win failure seems related to binding generator so probably unrelated to that change.
Committed r264698: <https://trac.webkit.org/changeset/264698> All reviewed patches have been landed. Closing bug and clearing flags on attachment 404906 [details].