Ensure the 1993 NTP logs to UMA Most Visited tiles that use the fallback thumbnail instead of the p…

chrome/browser/resources/local_ntp/most_visited_thumbnail.js

 // Copyright 2013 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 
 /**
  * @fileoverview Rendering for iframed most visited thumbnails.
  */
 
 window.addEventListener('DOMContentLoaded', function() {
@@ skipping 33 matching lines @@
       // thumbnail errors. The backup thumbnail is always preloaded so that the
       // server can't gain knowledge on the local thumbnail DB by specifying a
       // second URL that is only sometimes fetched.
       if (data.thumbnailUrl2) {
         var image2 = createAndAppendThumbnail(false);
         image2.onerror = showDomainElement;
         image2.src = data.thumbnailUrl2;
         // The first thumbnail's onerror function will swap the visibility of
         // the two thumbnails.
         image.onerror = function() {
+          logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_FALLBACK);

[Mathieu, 2013/09/03 21:40:23]

NTP_FALLBACK_THUMBNAIL_USED?

[beaudoin, 2013/09/03 22:34:55]

Done.

           image.style.visibility = 'hidden';
           image2.style.visibility = 'visible';
         };
+        logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_WITH_FALLBACK_ATTEMPT);

[Mathieu, 2013/09/03 21:40:23]

nit: NTP_FALLBACK_THUMBNAIL_REQUESTED to be closer to what's happening?

[beaudoin, 2013/09/03 22:34:55]

Done.

       } else {
         image.onerror = showDomainElement;
       }
       image.src = data.thumbnailUrl;
       logEvent(NTP_LOGGING_EVENT_TYPE.NTP_THUMBNAIL_ATTEMPT);
     } else {
       showDomainElement();
     }
   });
 });