mash: Create system tray display and rotation lock items via delegate

ash/system/tray/system_tray.h

Index: ash/system/tray/system_tray.h
diff --git a/ash/system/tray/system_tray.h b/ash/system/tray/system_tray.h
index 0bb4e657e5a821ebf70467ff5d2db7a9429d8963..97e34724b9ff4315dacfc48d06b468e59da2d18f 100644
--- a/ash/system/tray/system_tray.h
+++ b/ash/system/tray/system_tray.h
@@ -51,12 +51,9 @@ class ASH_EXPORT SystemTray : public TrayBackgroundView,
   // Resets internal pointers.
   void Shutdown();
 
-  // Adds a new item in the tray.
+  // Adds a new item in the tray. Takes ownership.
   void AddTrayItem(SystemTrayItem* item);
 
-  // Removes an existing tray item.
-  void RemoveTrayItem(SystemTrayItem* item);
-
   // Returns all tray items that has been added to system tray.
   const std::vector<SystemTrayItem*>& GetTrayItems() const;