Revert of mash: Remove ChromeLauncherController's |id_to_item_controller_map_|.

ash/common/shelf/shelf_model_observer.h

 // Copyright 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 ASH_COMMON_SHELF_SHELF_MODEL_OBSERVER_H_
 #define ASH_COMMON_SHELF_SHELF_MODEL_OBSERVER_H_
 
 #include "ash/ash_export.h"
 #include "ash/public/cpp/shelf_types.h"
 
 namespace ash {
 
 struct ShelfItem;
+class ShelfItemDelegate;
 
 class ASH_EXPORT ShelfModelObserver {
  public:
   // Invoked after an item has been added to the model.
   virtual void ShelfItemAdded(int index) = 0;
 
   // Invoked after an item has been removed from the model. |index| is the index
   // the item was at before removal, |old_item| is the item before removal.
   virtual void ShelfItemRemoved(int index, const ShelfItem& old_item) = 0;
 
   // Invoked after an item has been moved. See ShelfModel::Move() for details
   // of the arguments.
   virtual void ShelfItemMoved(int start_index, int target_index) = 0;
 
-  // Invoked after an item changes. |old_item| is the item before the change.
+  // Invoked when the state of an item changes. |old_item| is the item
+  // before the change.
   virtual void ShelfItemChanged(int index, const ShelfItem& old_item) = 0;
 
+  // Gets called when a ShelfItemDelegate gets changed. Note that
+  // |item_delegate| can be null.
+  // NOTE: This is added a temporary fix for M39 to fix crbug.com/429870.
+  // TODO(skuhne): Find the real reason for this problem and remove this fix.
+  virtual void OnSetShelfItemDelegate(ShelfID id,
+                                      ShelfItemDelegate* item_delegate) = 0;
+
  protected:
   virtual ~ShelfModelObserver() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_SHELF_MODEL_OBSERVER_H_