Use container::back() and container::pop_back() in ui/

ui/message_center/popup_timers_controller.cc

 // Copyright 2016 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 "ui/message_center/popup_timers_controller.h"
 
 #include <algorithm>
 
 #include "base/stl_util.h"
 #include "ui/message_center/message_center_style.h"
@@ skipping 78 matching lines @@
 void PopupTimersController::OnNotificationDisplayed(
     const std::string& id,
     const DisplaySource source) {
   OnNotificationUpdated(id);
 }
 
 void PopupTimersController::OnNotificationUpdated(const std::string& id) {
   NotificationList::PopupNotifications popup_notifications =
       message_center_->GetPopupNotifications();
 
-  if (!popup_notifications.size()) {
+  if (popup_notifications.empty()) {
     CancelAll();
     return;
   }
 
   NotificationList::PopupNotifications::const_iterator iter =
       popup_notifications.begin();
   for (; iter != popup_notifications.end(); ++iter) {
     if ((*iter)->id() == id)
       break;
   }
 
   if (iter == popup_notifications.end() || (*iter)->never_timeout()) {
     CancelTimer(id);
     return;
   }
 
   // Start the timer if not yet.
   if (popup_timers_.find(id) == popup_timers_.end())
     StartTimer(id, GetTimeoutForNotification(*iter));
 }
 
 void PopupTimersController::OnNotificationRemoved(const std::string& id,
                                                   bool by_user) {
   CancelTimer(id);
 }
 
 }  // namespace message_center