Integrate audible tab tracking into desktop engagement service.

chrome/browser/ui/browser_list_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 CHROME_BROWSER_UI_BROWSER_LIST_OBSERVER_H_
 #define CHROME_BROWSER_UI_BROWSER_LIST_OBSERVER_H_
 
 class Browser;
 
 namespace chrome {
 
 class BrowserListObserver {
   public:
   // Called immediately after a browser is added to the list
   virtual void OnBrowserAdded(Browser* browser) {}
 
   // Called immediately after a browser is removed from the list
   virtual void OnBrowserRemoved(Browser* browser) {}
 
   // Called immediately after a browser is set active (SetLastActive)
   virtual void OnBrowserSetLastActive(Browser* browser) {}
 
+  virtual void OnBrowserNoLongerActive(Browser* browser) {}
+
  protected:
   virtual ~BrowserListObserver() {}
 };
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_UI_BROWSER_LIST_OBSERVER_H_