Add presubmit check for scoped_ptr usage.

ui/message_center/views/notification_view_unittest.cc

 // Copyright 2014 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/views/notification_view.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/strings/utf_string_conversions.h"
 #include "testing/gtest/include/gtest/gtest.h"
 #include "third_party/skia/include/core/SkBitmap.h"
@@ skipping 144 matching lines @@
     bool by_user) {
   // For this test, this method should not be invoked.
   NOTREACHED();
 }
 
 scoped_ptr<ui::MenuModel> NotificationViewTest::CreateMenuModel(
     const NotifierId& notifier_id,
     const base::string16& display_source) {
   // For this test, this method should not be invoked.
   NOTREACHED();
-  return scoped_ptr<ui::MenuModel>();
+  return nullptr;
 }
 
 bool NotificationViewTest::HasClickedListener(
     const std::string& notification_id) {
   return true;
 }
 
 void NotificationViewTest::ClickOnNotificationButton(
     const std::string& notification_id,
     int button_index) {
@@ skipping 147 matching lines @@
 
   // Double-check that vertical order is correct.
   CheckVerticalOrderInNotification();
 
   // Tests that views remain in that order even after an update.
   UpdateNotificationViews();
   CheckVerticalOrderInNotification();
 }
 
 }  // namespace message_center