Fix UMA collection of webfont CORS

We should check actual failures of webfont CORS because
|options().corsEnabled| won't set when the webfont has the same
origin.

BUG=286681

Review URL: https://codereview.chromium.org/239983002

git-svn-id: svn://svn.chromium.org/blink/trunk@172095 bbb929c8-8fbe-4397-9dbb-9b2b20218538