ash: Remove ShelfModel id conversion functions.

ash/shelf/shelf_view.h

 // Copyright (c) 2012 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_SHELF_SHELF_VIEW_H_
 #define ASH_SHELF_SHELF_VIEW_H_
 
 #include <memory>
 #include <string>
 #include <utility>
@@ skipping 413 matching lines @@
   // The timestamp of the last shelf item touch press event.
   base::TimeTicks touch_press_time_;
 
   // True if a drag and drop operation created/pinned the item in the launcher
   // and it needs to be deleted/unpinned again if the operation gets cancelled.
   bool drag_and_drop_item_pinned_ = false;
 
   // The ShelfItem currently used for drag and drop; empty if none.
   ShelfID drag_and_drop_shelf_id_;
 
-  // The application ID of the application which we drag and drop.
-  std::string drag_and_drop_app_id_;
-
   // The original launcher item's size before the dragging operation.
   gfx::Size pre_drag_and_drop_size_;
 
   // The image proxy for drag operations when a drag and drop host exists and
   // the item can be dragged outside the app grid.
   std::unique_ptr<ash::DragImageView> drag_image_;
 
   // The cursor offset to the middle of the dragged item.
   gfx::Vector2d drag_image_offset_;
 
@@ skipping 31 matching lines @@
   ShelfButtonPressedMetricTracker shelf_button_pressed_metric_tracker_;
 
   base::WeakPtrFactory<ShelfView> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfView);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_VIEW_H_