Allow partial update for notification update API

chrome/browser/notifications/notification.cc

 // Copyright (c) 2012 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/notifications/notification.h"
 
 #include "base/strings/string_util.h"
 #include "chrome/browser/notifications/desktop_notification_service.h"
 #include "ui/message_center/message_center_util.h"
 #include "ui/webui/web_ui_util.h"
 
+Notification::Notification() {
+}
+
 Notification::Notification(const GURL& origin_url,
                            const GURL& content_url,
                            const string16& display_source,
                            const string16& replace_id,
                            NotificationDelegate* delegate)
     : message_center::Notification(message_center::NOTIFICATION_TYPE_SIMPLE,
                                    delegate->id(),
                                    EmptyString16(),
                                    EmptyString16(),
                                    gfx::Image(),
@@ skipping 111 matching lines @@
   icon_url_ = notification.icon_url();
   is_html_ = notification.is_html();
   content_url_ = notification.content_url();
   button_one_icon_url_ = notification.button_one_icon_url();
   button_two_icon_url_ = notification.button_two_icon_url();
   image_url_ = notification.image_url();
   replace_id_ = notification.replace_id();
   delegate_ = notification.delegate();
   return *this;
 }