reland: mash: Remove ChromeLauncherController's |id_to_item_controller_map_|.

ash/shelf/shelf_model.h

Index: ash/shelf/shelf_model.h
diff --git a/ash/shelf/shelf_model.h b/ash/shelf/shelf_model.h
index 53f1977b25ce586af9514fbf4d95db8b6ee5dfc0..b3bb09eb077cfb3298fbb2f0b3e09c9404103794 100644
--- a/ash/shelf/shelf_model.h
+++ b/ash/shelf/shelf_model.h
@@ -92,9 +92,6 @@ class ASH_EXPORT ShelfModel {
   // returns the new value.
   int ValidateInsertionIndex(ShelfItemType type, int index) const;
 
-  // Remove and destroy ShelfItemDelegate for |id|.
-  void RemoveShelfItemDelegate(ShelfID id);
-
   // ID assigned to the next item.
   ShelfID next_id_;