Move message_center::CustomNotificationView to arc::ArcNotificationView

ui/arc/notification/arc_notification_item_impl.cc

 // Copyright 2017 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/arc/notification/arc_notification_item_impl.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/memory/ptr_util.h"
@@ skipping 173 matching lines @@
 
 mojom::ArcNotificationShownContents ArcNotificationItemImpl::GetShownContents()
     const {
   return shown_contents_;
 }
 
 const std::string& ArcNotificationItemImpl::GetNotificationKey() const {
   return notification_key_;
 }
 
+const std::string& ArcNotificationItemImpl::GetNotificationId() const {
+  return notification_id_;
+}
+
 }  // namespace arc