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

chrome/browser/devtools/global_confirm_info_bar.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/devtools/global_confirm_info_bar.h"
 
 #include <utility>
 
 #include "base/macros.h"
 #include "chrome/browser/ui/browser.h"
@@ skipping 142 matching lines @@
 GlobalConfirmInfoBar::~GlobalConfirmInfoBar() {
   while (!proxies_.empty()) {
     auto it = proxies_.begin();
     it->second->Detach();
     it->first->RemoveObserver(this);
     it->first->RemoveInfoBar(it->second->info_bar_);
     proxies_.erase(it);
   }
 }
 
-void GlobalConfirmInfoBar::TabInsertedAt(content::WebContents* web_contents,
+// Do not use |tab_strip_model| as it may be null from the call in
+// TabChangedAt().
+void GlobalConfirmInfoBar::TabInsertedAt(TabStripModel* tab_strip_model,
+                                         content::WebContents* web_contents,
                                          int index,
                                          bool foreground) {
   InfoBarService* infobar_service =
       InfoBarService::FromWebContents(web_contents);
   // WebContents from the tab strip must have the infobar service.
   DCHECK(infobar_service);
   if (proxies_.find(infobar_service) != proxies_.end())
       return;
 
   std::unique_ptr<GlobalConfirmInfoBar::DelegateProxy> proxy(
       new GlobalConfirmInfoBar::DelegateProxy(weak_factory_.GetWeakPtr()));
   GlobalConfirmInfoBar::DelegateProxy* proxy_ptr = proxy.get();
   infobars::InfoBar* added_bar = infobar_service->AddInfoBar(
       infobar_service->CreateConfirmInfoBar(std::move(proxy)));
 
   proxy_ptr->info_bar_ = added_bar;
   DCHECK(added_bar);
   proxies_[infobar_service] = proxy_ptr;
   infobar_service->AddObserver(this);
 }
 
 void GlobalConfirmInfoBar::TabChangedAt(content::WebContents* web_contents,
                                         int index,
                                         TabChangeType change_type) {
   InfoBarService* infobar_service =
       InfoBarService::FromWebContents(web_contents);
   auto it = proxies_.find(infobar_service);
   if (it == proxies_.end())
-    TabInsertedAt(web_contents, index, false);
+    TabInsertedAt(nullptr, web_contents, index, false);
 }
 
 void GlobalConfirmInfoBar::OnInfoBarRemoved(infobars::InfoBar* info_bar,
                                             bool animate) {
   // Do not process alien infobars.
   for (auto it : proxies_) {
     if (it.second->info_bar_ == info_bar) {
       OnManagerShuttingDown(info_bar->owner());
       break;
     }
   }
 }
 
 void GlobalConfirmInfoBar::OnManagerShuttingDown(
     infobars::InfoBarManager* manager) {
   manager->RemoveObserver(this);
   proxies_.erase(manager);
 }