Implement the Notification `timestamp` property

content/public/common/platform_notification_data.h

 // 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.
 
 #ifndef CONTENT_PUBLIC_COMMON_PLATFORM_NOTIFICATION_DATA_H_
 #define CONTENT_PUBLIC_COMMON_PLATFORM_NOTIFICATION_DATA_H_
 
 #include <stddef.h>
 
 #include <string>
 #include <vector>
 
 #include "base/strings/string16.h"
+#include "base/time/time.h"
 #include "content/common/content_export.h"
 #include "url/gurl.h"
 
 namespace content {
 
 // A notification action (button); corresponds to Blink WebNotificationAction.
 struct CONTENT_EXPORT PlatformNotificationAction {
   PlatformNotificationAction();
   ~PlatformNotificationAction();
 
@@ skipping 39 matching lines @@
   // tag will replace the first displayed notification.
   std::string tag;
 
   // URL of the icon which is to be displayed with the notification.
   GURL icon;
 
   // Vibration pattern for the notification, following the syntax of the
   // Vibration API. https://www.w3.org/TR/vibration/
   std::vector<int> vibration_pattern;
 
+  // The time at which the event the notification represents took place.
+  base::Time timestamp;
+
   // Whether default notification indicators (sound, vibration, light) should
   // be suppressed.
   bool silent = false;
 
   // Whether the notification should remain onscreen indefinitely, rather than
   // being auto-minimized to the notification center (if allowed by platform).
   bool require_interaction = false;
 
   // Developer-provided data associated with the notification, in the form of
   // a serialized string. Must not exceed |kMaximumDeveloperDataSize| bytes.
   std::vector<char> data;
 
   // Actions that should be shown as buttons on the notification.
   std::vector<PlatformNotificationAction> actions;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_PLATFORM_NOTIFICATION_DATA_H_