Add UMA histograms for Google cached copy experiment on network error interstitial

chrome/renderer/resources/neterror.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.
 
 function toggleHelpBox() {
   var helpBoxOuter = document.getElementById('details');
   helpBoxOuter.classList.toggle('hidden');
   var detailsButton = document.getElementById('details-button');
   if (helpBoxOuter.classList.contains('hidden'))
     detailsButton.innerText = detailsButton.detailsText;
@@ skipping 107 matching lines @@
  */
 function setUpCachedButton(buttonStrings) {
   var reloadButton = document.getElementById('reload-button');
 
   reloadButton.textContent = buttonStrings.msg;
   var url = buttonStrings.cacheUrl;
   var trackingId = buttonStrings.trackingId;
   reloadButton.onclick = function(e) {
     e.preventDefault();
     trackClick(trackingId);
+    if (window.errorPageController) {
+      errorPageController.trackCachedCopyButtonClick(
+          buttonStrings.defaultLabel);
+    }
     location = url;
   };
   reloadButton.style.display = '';
   document.getElementById('control-buttons').hidden = false;
 }
 
 var primaryControlOnLeft = true;
 <if expr="is_macosx or is_ios or is_linux or is_android">
 primaryControlOnLeft = false;
 </if>
@@ skipping 58 matching lines @@
     p.hidden = false;
   }
 
   // Check for Google cached copy suggestion.
   if (loadTimeData.valueExists('cacheButton')) {
     setUpCachedButton(loadTimeData.getValue('cacheButton'));
   }
 }
 
 document.addEventListener('DOMContentLoaded', onDocumentLoad);