Always report access control failure if accessing unsupported URL.

For attempted cross-origin requests to unsupported CORS URLs, extend the
error reporting to also apply to non-simple requests that would require
a preflight. It is also bound to fail.

R=abarth@chromium.org,tyoshino@chromium.org
BUG=389751

Review URL: https://codereview.chromium.org/389053003

git-svn-id: svn://svn.chromium.org/blink/trunk@178091 bbb929c8-8fbe-4397-9dbb-9b2b20218538