Add metrics to keep track of the tab activate/deactivate cycle

chrome/browser/ui/unload_controller.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_UNLOAD_CONTROLLER_H_
 #define CHROME_BROWSER_UI_UNLOAD_CONTROLLER_H_
 
 #include <set>
 
 #include "base/callback.h"
@@ skipping 74 matching lines @@
 
  private:
   typedef std::set<content::WebContents*> UnloadListenerSet;
 
   // Overridden from content::NotificationObserver:
   void Observe(int type,
                const content::NotificationSource& source,
                const content::NotificationDetails& details) override;
 
   // Overridden from TabStripModelObserver:
-  void TabInsertedAt(content::WebContents* contents,
+  void TabInsertedAt(TabStripModel* tab_strip_model,
+                     content::WebContents* contents,
                      int index,
                      bool foreground) override;
   void TabDetachedAt(content::WebContents* contents, int index) override;
   void TabReplacedAt(TabStripModel* tab_strip_model,
                      content::WebContents* old_contents,
                      content::WebContents* new_contents,
                      int index) override;
   void TabStripEmpty() override;
 
   void TabAttachedImpl(content::WebContents* contents);
@@ skipping 49 matching lines @@
   base::Callback<void(bool)> on_close_confirmed_;
 
   base::WeakPtrFactory<UnloadController> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(UnloadController);
 };
 
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_UI_UNLOAD_CONTROLLER_H_