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..ca8f405434a81ba7c7ee2569eaa1e64b4c3bfc2d 100644
--- a/ash/shelf/shelf_model_observer.h
+++ b/ash/shelf/shelf_model_observer.h
@@ -11,7 +11,9 @@
 namespace ash {
 
 struct ShelfItem;
+class ShelfItemDelegate;
 
+// TODO(msw): Move this to ash/public/cpp and use ASH_PUBLIC_EXPORT.
 class ASH_EXPORT ShelfModelObserver {
  public:
   // Invoked after an item has been added to the model.
@@ -28,6 +30,10 @@ 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() {}
 };