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

chrome/browser/ui/unload_controller.cc

 // 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.
 
 #include "chrome/browser/ui/unload_controller.h"
 
 #include "base/location.h"
 #include "base/single_thread_task_runner.h"
 #include "base/threading/thread_task_runner_handle.h"
 #include "chrome/browser/chrome_notification_types.h"
@@ skipping 207 matching lines @@
 
   if (is_attempting_to_close_browser_) {
     ClearUnloadState(content::Source<content::WebContents>(source).ptr(),
                      false);  // See comment for ClearUnloadState().
   }
 }
 
 ////////////////////////////////////////////////////////////////////////////////
 // UnloadController, TabStripModelObserver implementation:
 
-void UnloadController::TabInsertedAt(content::WebContents* contents,
+void UnloadController::TabInsertedAt(TabStripModel* tab_strip_model,
+                                     content::WebContents* contents,
                                      int index,
                                      bool foreground) {
   TabAttachedImpl(contents);
 }
 
 void UnloadController::TabDetachedAt(content::WebContents* contents,
                                      int index) {
   TabDetachedImpl(contents);
 }
 
@@ skipping 121 matching lines @@
       ProcessPendingTabs();
     } else {
       base::ThreadTaskRunnerHandle::Get()->PostTask(
           FROM_HERE, base::Bind(&UnloadController::ProcessPendingTabs,
                                 weak_factory_.GetWeakPtr()));
     }
   }
 }
 
 }  // namespace chrome