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

chrome/browser/ui/tabs/tab_strip_model_observer.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/tabs/tab_strip_model_observer.h"
 
 using content::WebContents;
 
-void TabStripModelObserver::TabInsertedAt(WebContents* contents,
+void TabStripModelObserver::TabInsertedAt(TabStripModel* tab_strip_model,
+                                          WebContents* contents,
                                           int index,
                                           bool foreground) {
 }
 
 void TabStripModelObserver::TabClosingAt(TabStripModel* tab_strip_model,
                                          WebContents* contents,
                                          int index) {
 }
 
 void TabStripModelObserver::TabDetachedAt(WebContents* contents,
@@ skipping 23 matching lines @@
                                          int index,
                                          TabChangeType change_type) {
 }
 
 void TabStripModelObserver::TabReplacedAt(TabStripModel* tab_strip_model,
                                           WebContents* old_contents,
                                           WebContents* new_contents,
                                           int index) {
 }
 
-void TabStripModelObserver::TabPinnedStateChanged(WebContents* contents,
-                                                  int index) {
+void TabStripModelObserver::TabPinnedStateChanged(
+    TabStripModel* tab_strip_model,
+    WebContents* contents,
+    int index) {
 }
 
 void TabStripModelObserver::TabBlockedStateChanged(WebContents* contents,
                                                    int index) {
 }
 
 void TabStripModelObserver::TabStripEmpty() {
 }
 
 void TabStripModelObserver::WillCloseAllTabs() {
 }
 
 void TabStripModelObserver::CloseAllTabsCanceled() {
 }