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 foo*bar/baz+xml
PASS successfullyParsed is true

TEST COMPLETE