mash: Fix ShelfItem mojo struct; add enums and traits.

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/common/shelf/shelf_item_types.h"
+#include "ash/public/cpp/shelf_item.h"
 
 namespace ash {
 
 struct ShelfItem;
 
 namespace mojom {
 class ShelfItemDelegate;
 }
 
 class ASH_EXPORT ShelfModelObserver {
@@ skipping 21 matching lines @@
       ShelfID id,
       mojom::ShelfItemDelegate* item_delegate) = 0;
 
  protected:
   virtual ~ShelfModelObserver() {}
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SHELF_SHELF_MODEL_OBSERVER_H_