Re-enable WebFont.CORSSuccess histogram

We want to keep this histogram for a while.

BUG=286681

Review URL: https://codereview.chromium.org/335123004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@278030 0039d316-1c4b-4281-b951-d872f2087c98

tools/metrics/histograms/histograms.xml

@@ -32409,9 +32409,6 @@ Therefore, the affected-histogram name has to have at least one dot in it.
 </histogram>
 
 <histogram name="WebFont.CORSSuccess" enum="BooleanSuccess">
-  <obsolete>
-    Removed from code as of 2014/06/10.
-  </obsolete>
   <owner>bashi@chromium.org</owner>
   <owner>kenjibaheux@chromium.org</owner>
   <summary>The success or failure of web fonts CORS-enabled fetching.</summary>