Import fetch/stale-while-revalidate/fetch.html to try to fix flakiness (see https://bugs.webkit.org/show_bug.cgi?id=207230).
Created attachment 397332 [details] Patch
Created attachment 397354 [details] Patch
Committed r260624: <https://trac.webkit.org/changeset/260624> All reviewed patches have been landed. Closing bug and clearing flags on attachment 397354 [details].
<rdar://problem/62290449>