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

chrome/browser/memory/tab_manager.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_MEMORY_TAB_MANAGER_H_
 #define CHROME_BROWSER_MEMORY_TAB_MANAGER_H_
 
 #include <stdint.h>
 
 #include <memory>
@@ skipping 246 matching lines @@
       base::MemoryPressureListener::MemoryPressureLevel memory_pressure_level);
 
   // TabStripModelObserver overrides.
   void TabChangedAt(content::WebContents* contents,
                     int index,
                     TabChangeType change_type) override;
   void ActiveTabChanged(content::WebContents* old_contents,
                         content::WebContents* new_contents,
                         int index,
                         int reason) override;
-  void TabInsertedAt(content::WebContents* contents,
+  void TabInsertedAt(TabStripModel* tab_strip_model,
+                     content::WebContents* contents,
                      int index,
                      bool foreground) override;
 
   // Returns true if the tab is currently playing audio or has played audio
   // recently, or if the tab is currently accessing the camera, microphone or
   // mirroring the display.
   bool IsMediaTab(content::WebContents* contents) const;
 
   // Returns the WebContentsData associated with |contents|. Also takes care of
   // creating one if needed.
@@ skipping 100 matching lines @@
 
   // Weak pointer factory used for posting delayed tasks to task_runner_.
   base::WeakPtrFactory<TabManager> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(TabManager);
 };
 
 }  // namespace memory
 
 #endif  // CHROME_BROWSER_MEMORY_TAB_MANAGER_H_