XMLHttpRequest must build a request using the given method as-is for non-standard types

As per step-5 of http://xhr.spec.whatwg.org/#the-open()-method only DELETE, PUT, GET, POST, OPTIONS, HEAD are standard. Use other methods as is without case change.
We now pass all cases from w3c-test : http://w3c-test.org/XMLHttpRequest/open-method-case-sensitive.htm.

BUG=386347
TEST=http/tests/xmlhttprequest/xmlhttprequest-open-method-allowed.html

Review URL: https://codereview.chromium.org/347653003

git-svn-id: svn://svn.chromium.org/blink/trunk@176592 bbb929c8-8fbe-4397-9dbb-9b2b20218538