UMA for measuring how often 2 or more tabs script the same background contents.

content/public/browser/web_contents_observer.h

 // Copyright (c) 2012 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 CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 #define CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_
 
 #include <stdint.h>
 
 #include "base/macros.h"
@@ skipping 405 matching lines @@
   // Invoked when the renderer process changes the page scale factor.
   virtual void OnPageScaleFactorChanged(float page_scale_factor) {}
 
   // Invoked if an IPC message is coming from a specific RenderFrameHost.
   virtual bool OnMessageReceived(const IPC::Message& message,
                                  RenderFrameHost* render_frame_host);
 
   // Notification that |contents| has gained focus.
   virtual void OnWebContentsFocused() {}
 
+  // Notification that opener has changed.
+  virtual void DidChangeOpener() {}
+
   // Notifes that a CompositorFrame was received from the renderer.
   virtual void DidReceiveCompositorFrame() {}
 
   // IPC::Listener implementation.
   bool OnMessageReceived(const IPC::Message& message) override;
 
   // IPC::Sender implementation.
   bool Send(IPC::Message* message) override;
   int routing_id() const;
 
@@ skipping 20 matching lines @@
   void ResetWebContents();
 
   WebContentsImpl* web_contents_;
 
   DISALLOW_COPY_AND_ASSIGN(WebContentsObserver);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_BROWSER_WEB_CONTENTS_OBSERVER_H_