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

chrome/browser/ui/browser_tab_strip_tracker.cc

 // Copyright 2015 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/browser_tab_strip_tracker.h"
 
 #include "base/auto_reset.h"
 #include "chrome/browser/ui/browser.h"
 #include "chrome/browser/ui/browser_list.h"
 #include "chrome/browser/ui/browser_tab_strip_tracker_delegate.h"
@@ skipping 53 matching lines @@
   browsers_observing_.insert(browser);
 
   if (browser_list_observer_)
     browser_list_observer_->OnBrowserAdded(browser);
 
   TabStripModel* tab_strip_model = browser->tab_strip_model();
   tab_strip_model->AddObserver(tab_strip_model_observer_);
   const int active_index = tab_strip_model->active_index();
   for (int i = 0; i < tab_strip_model->count(); ++i) {
     tab_strip_model_observer_->TabInsertedAt(
-        tab_strip_model->GetWebContentsAt(i), i, i == active_index);
+        tab_strip_model, tab_strip_model->GetWebContentsAt(i), i,
+        i == active_index);
   }
 }
 
 void BrowserTabStripTracker::OnBrowserAdded(Browser* browser) {
   MaybeTrackBrowser(browser);
 }
 
 void BrowserTabStripTracker::OnBrowserRemoved(Browser* browser) {
   auto it = browsers_observing_.find(browser);
   if (it == browsers_observing_.end())
     return;
 
   browsers_observing_.erase(it);
   browser->tab_strip_model()->RemoveObserver(tab_strip_model_observer_);
 
   if (browser_list_observer_)
     browser_list_observer_->OnBrowserRemoved(browser);
 }
 
 void BrowserTabStripTracker::OnBrowserSetLastActive(Browser* browser) {
   if (browser_list_observer_)
     browser_list_observer_->OnBrowserSetLastActive(browser);
 }