Webfont CORS-enabled fetching with fallback

Use CORS-enabled fetch method for webfonts. If the CORS-enabled fetch
fails, make a second CORS-disabled request so that we won't break
existing webpages which don't honor the css3 font spec.

We also collect CORS failure counts.

BUG=286681
R=ksakamoto@chromium.org, japhet@chromium.org

Review URL: https://codereview.chromium.org/230383003

git-svn-id: svn://svn.chromium.org/blink/trunk@171423 bbb929c8-8fbe-4397-9dbb-9b2b20218538