Implement the Notification `timestamp` property

chrome/browser/notifications/platform_notification_service_impl.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 "chrome/browser/notifications/platform_notification_service_impl.h"
 
 #include <utility>
 #include <vector>
 
 #include "base/command_line.h"
@@ skipping 463 matching lines @@
       message_center::NOTIFICATION_TYPE_SIMPLE, notification_data.title,
       notification_data.body,
       gfx::Image::CreateFrom1xBitmap(notification_resources.notification_icon),
       message_center::NotifierId(origin), base::UTF8ToUTF16(origin.host()),
       origin, notification_data.tag, message_center::RichNotificationData(),
       delegate);
 
   notification.set_context_message(
       DisplayNameForContextMessage(profile, origin));
   notification.set_vibration_pattern(notification_data.vibration_pattern);
+  notification.set_timestamp(notification_data.timestamp);
   notification.set_silent(notification_data.silent);
 
   std::vector<message_center::ButtonInfo> buttons;
 
   // Developer supplied buttons.
   for (const auto& action : notification_data.actions)
     buttons.push_back(message_center::ButtonInfo(action.title));
 
   notification.set_buttons(buttons);
 
@@ skipping 55 matching lines @@
         extensions::ExtensionRegistry::Get(profile)->GetExtensionById(
             origin.host(), extensions::ExtensionRegistry::EVERYTHING);
     DCHECK(extension);
 
     return base::UTF8ToUTF16(extension->name());
   }
 #endif
 
   return base::string16();
 }