Start building message_center on Mac.

ui/message_center/message_center_tray_delegate.h

 // Copyright (c) 2013 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_MESSAGE_CENTER_TRAY_DELEGATE_H_
 #define UI_MESSAGE_CENTER_MESSAGE_CENTER_TRAY_DELEGATE_H_
 
+#include "ui/message_center/message_center_export.h"
+
 namespace message_center {
 
 // A MessageCenterTrayDelegate class is responsible for managing the various UI
 // surfaces that should be displayed when the MessageCenter is changed.
 class MESSAGE_CENTER_EXPORT MessageCenterTrayDelegate {
  public:
   virtual ~MessageCenterTrayDelegate() {};
 
   // Called whenever a change to the visible UI has occurred.
   virtual void OnMessageCenterTrayChanged() = 0;
@@ skipping 17 matching lines @@
   virtual void HideMessageCenter() = 0;
 
   // Called when a change to the message center could cause a change to the
   // message center widget that is currently being displayed.
   virtual void UpdateMessageCenter() = 0;
 };
 
 }  // namespace message_center
 
 #endif  // UI_MESSAGE_CENTER_MESSAGE_CENTER_TRAY_DELEGATE_H_