Resync web-platform-tests/xhr from upstream.
Created attachment 403819 [details] Patch
Comment on attachment 403819 [details] Patch r=me
Created attachment 403832 [details] Patch
Created attachment 403835 [details] Patch
Created attachment 403869 [details] Patch
Committed r264174: <https://trac.webkit.org/changeset/264174> All reviewed patches have been landed. Closing bug and clearing flags on attachment 403869 [details].
<rdar://problem/65274111>