Show message to indicate that mirriring with more than 3 display is not supported.

ash/display/display_util.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 ASH_DISPLAY_DISPLAY_UTIL_H_
 #define ASH_DISPLAY_DISPLAY_UTIL_H_
 
 #include <stdint.h>
 
 #include <set>
@@ skipping 105 matching lines @@
     const display::DisplayList& list);
 
 ASH_EXPORT std::string DisplayIdListToString(
     const display::DisplayIdList& list);
 
 // Returns true if one of following conditinos is met.
 // 1) id1 is internal.
 // 2) output index of id1 < output index of id2 and id2 isn't internal.
 ASH_EXPORT bool CompareDisplayIds(int64_t id1, int64_t id2);
 
+// Shows the notification message for display related issues.
+void ShowDisplayErrorNotification(int message_id);
+
+ASH_EXPORT base::string16 GetDisplayErrorNotificationMessageForTest();
+
 }  // namespace ash
 
 #endif  // ASH_DISPLAY_DISPLAY_UTIL_H_