Remove font fetching fallback for CORS failures

We are going to disallow CORS-disabled font fetching.
Also adding a test case to check whether CORS is working.

BUG=286681

Review URL: https://codereview.chromium.org/316353003

git-svn-id: svn://svn.chromium.org/blink/trunk@175927 bbb929c8-8fbe-4397-9dbb-9b2b20218538