Fix linker error due to missing MESSAGE_CENTER_EXPORT

ui/message_center/notification_list.h

 // 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.
 
 #ifndef UI_MESSAGE_CENTER_NOTIFICATION_LIST_H_
 #define UI_MESSAGE_CENTER_NOTIFICATION_LIST_H_
 
 #include <list>
 #include <set>
 #include <string>
@@ skipping 20 matching lines @@
 
 class Notification;
 class NotificationDelegate;
 struct NotifierId;
 
 // Comparers used to auto-sort the lists of Notifications.
 struct MESSAGE_CENTER_EXPORT ComparePriorityTimestampSerial {
   bool operator()(Notification* n1, Notification* n2);
 };
 
-struct CompareTimestampSerial {
+struct MESSAGE_CENTER_EXPORT CompareTimestampSerial {
   bool operator()(Notification* n1, Notification* n2);
 };
 
 // A helper class to manage the list of notifications.
 class MESSAGE_CENTER_EXPORT NotificationList {
  public:
   // Auto-sorted set. Matches the order in which Notifications are shown in
   // Notification Center.
   typedef std::set<Notification*, ComparePriorityTimestampSerial> Notifications;
 
@@ skipping 98 matching lines @@
   Notifications notifications_;
   bool message_center_visible_;
   bool quiet_mode_;
 
   DISALLOW_COPY_AND_ASSIGN(NotificationList);
 };
 
 }  // namespace message_center
 
 #endif // UI_MESSAGE_CENTER_NOTIFICATION_LIST_H_