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

chrome/renderer/net/net_error_page_controller.h

 // Copyright 2014 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.
 
 #ifndef CHROME_RENDERER_NET_NET_ERROR_PAGE_CONTROLLER_H_
 #define CHROME_RENDERER_NET_NET_ERROR_PAGE_CONTROLLER_H_
 
 #include "base/macros.h"
 #include "components/error_page/renderer/net_error_helper_core.h"
 #include "content/public/renderer/render_frame_observer.h"
@@ skipping 25 matching lines @@
 
   // Execute a "Reload" button click.
   bool ReloadButtonClick();
 
   // Execute a "Details" button click.
   bool DetailsButtonClick();
 
   // Track easter egg plays.
   bool TrackEasterEgg();
 
+  // Track "Show cached copy/page" button clicks.
+  bool TrackCachedCopyButtonClick(bool is_default_label);
+
   // Track a click when the page has suggestions from the navigation correction
   // service.
   bool TrackClick(const gin::Arguments& args);
 
   // Used internally by other button click methods.
   bool ButtonClick(error_page::NetErrorHelperCore::Button button);
 
   // gin::WrappableBase
   gin::ObjectTemplateBuilder GetObjectTemplateBuilder(
       v8::Isolate* isolate) override;
 
   // RenderFrameObserver.  Overridden to avoid being destroyed when RenderFrame
   // goes away; NetErrorPageController objects are owned by the JS
   // garbage collector.
   void OnDestruct() override;
 
   DISALLOW_COPY_AND_ASSIGN(NetErrorPageController);
 };
 
 #endif  // CHROME_RENDERER_NET_NET_ERROR_PAGE_CONTROLLER_H_