Remove responseIsXML method, it can be inlined and is still readable, also it in one case this avoids calling the non trivial responseMIMEType.
Created attachment 410139 [details] Patch
Committed r267821: <https://trac.webkit.org/changeset/267821> All reviewed patches have been landed. Closing bug and clearing flags on attachment 410139 [details].
<rdar://problem/69824720>