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

ui/message_center/notification_list_unittest.cc

Index: ui/message_center/notification_list_unittest.cc
diff --git a/ui/message_center/notification_list_unittest.cc b/ui/message_center/notification_list_unittest.cc
index aad9154beeaf932ed65a84f92143942e1257df84..9daa10310629a1a939fcdbb68a49c95f1864b376 100644
--- a/ui/message_center/notification_list_unittest.cc
+++ b/ui/message_center/notification_list_unittest.cc
@@ -295,8 +295,8 @@ TEST_F(NotificationListTest, OldPopupShouldNotBeHidden) {
   }
   popups.clear();
   popups = GetPopups();
-  EXPECT_EQ(1u, popups.size());
-  EXPECT_EQ(ids[ids.size() - 1], (*popups.begin())->id());
+  ASSERT_EQ(1u, popups.size());
+  EXPECT_EQ(ids.back(), (*popups.begin())->id());
 }
 
 TEST_F(NotificationListTest, Priority) {