Test identification of XML content type in XHR responses.
On success, you will see a series of "PASS" messages, followed by "TEST COMPLETE".
PASS foo bar/baz+xml
PASS foo[bar/baz+xml
PASS foo]bar/baz+xml
PASS foo(bar/baz+xml
PASS foo)bar/baz+xml
PASS foo<bar/baz+xml
PASS foo>bar/baz+xml
PASS foo@bar/baz+xml
PASS successfullyParsed is true
TEST COMPLETE