Remove a bunch of broken/unused/non-useful NTP UMA histograms

chrome/browser/resources/local_ntp/most_visited_util.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 Utilities for rendering most visited thumbnails and titles.
  */
 
 <include src="instant_iframe_validation.js">
@@ skipping 12 matching lines @@
  * @const
  */
 var NTP_LOGGING_EVENT_TYPE = {
   // The suggestion is coming from the server.
   NTP_SERVER_SIDE_SUGGESTION: 0,
   // The suggestion is coming from the client.
   NTP_CLIENT_SIDE_SUGGESTION: 1,
   // Indicates a tile was rendered, no matter if it's a thumbnail, a gray tile
   // or an external tile.
   NTP_TILE: 2,
-  // The tile uses a local thumbnail image.
-  NTP_THUMBNAIL_TILE: 3,
-  // Used when no thumbnail is specified and a gray tile with the domain is used
-  // as the main tile.
-  NTP_GRAY_TILE: 4,
-  // The visuals of that tile are handled externally by the page itself.
-  NTP_EXTERNAL_TILE: 5,
-  // There was an error in loading both the thumbnail image and the fallback
-  // (if it was provided), resulting in a grey tile.
-  NTP_THUMBNAIL_ERROR: 6,
-  // Used a gray tile with the domain as the fallback for a failed thumbnail.
-  NTP_GRAY_TILE_FALLBACK: 7,
-  // The visuals of that tile's fallback are handled externally.
-  NTP_EXTERNAL_TILE_FALLBACK: 8,
   // A NTP Tile has finished loading (successfully or failing).
   NTP_TILE_LOADED: 10,
 };
 
 /**
  * The different sources that an NTP tile can have.
  * Note: Keep in sync with common/ntp_logging_events.h
  * @enum {number}
  * @const
  */
@@ skipping 244 matching lines @@
   if (navigator.sendBeacon) {
     navigator.sendBeacon(url);
   } else {
     // if sendBeacon is not enabled, we fallback for "a ping".
     var a = document.createElement('a');
     a.href = '#';
     a.ping = url;
     a.click();
   }
 }