Add thread-checker for public methods of message center

ui/message_center/message_center_impl.h

Index: ui/message_center/message_center_impl.h
diff --git a/ui/message_center/message_center_impl.h b/ui/message_center/message_center_impl.h
index a167a70b1d00e863b0abce744af6b61e2a9b8395..3dd9c7f349a629e8b6846e8f8b1a2a28d8717e90 100644
--- a/ui/message_center/message_center_impl.h
+++ b/ui/message_center/message_center_impl.h
@@ -13,6 +13,7 @@
 
 #include "base/macros.h"
 #include "base/memory/weak_ptr.h"
+#include "base/threading/thread_checker.h"
 #include "base/time/time.h"
 #include "base/timer/timer.h"
 #include "ui/message_center/message_center.h"
@@ -119,6 +120,8 @@ class MessageCenterImpl : public MessageCenter,
 
   void RemoveNotificationsForNotifierId(const NotifierId& notifier_id);
 
+  THREAD_CHECKER(thread_checker_);
+
   std::unique_ptr<NotificationList> notification_list_;
   NotificationCache notification_cache_;
   base::ObserverList<MessageCenterObserver> observer_list_;