mash: Support ShelfModel access in Chrome.

ash/shelf/shelf_model_observer.h

Index: ash/shelf/shelf_model_observer.h
diff --git a/ash/shelf/shelf_model_observer.h b/ash/shelf/shelf_model_observer.h
index fafb45c707e77b1c19f2e8e50837039ebb1c5de1..6857c601816830bd0f669affab625a8c26b3afa2 100644
--- a/ash/shelf/shelf_model_observer.h
+++ b/ash/shelf/shelf_model_observer.h
@@ -11,6 +11,7 @@
 namespace ash {
 
 struct ShelfItem;
+class ShelfItemDelegate;
 
 class ASH_EXPORT ShelfModelObserver {
  public:
@@ -28,6 +29,10 @@ class ASH_EXPORT ShelfModelObserver {
   // Invoked after an item changes. |old_item| is the item before the change.
   virtual void ShelfItemChanged(int index, const ShelfItem& old_item) = 0;
 
+  // Invoked after a delegate changes. |delegate| is the new value.
+  virtual void ShelfItemDelegateChanged(const ShelfID& id,
+                                        ShelfItemDelegate* delegate) = 0;
+
  protected:
   virtual ~ShelfModelObserver() {}
 };