Make shelf item can be dragged when context menu is opened.

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 297 matching lines @@
   void ShelfItemRemoved(int model_index, const ShelfItem& old_item) override;
   void ShelfItemChanged(int model_index, const ShelfItem& old_item) override;
   void ShelfItemMoved(int start_index, int target_index) override;
   void ShelfItemDelegateChanged(const ShelfID& id,
                                 ShelfItemDelegate* delegate) override;
 
   // Handles the result when querying ShelfItemDelegates for context menu items.
   // Shows a default shelf context menu with optional extra custom |menu_items|.
   void AfterGetContextMenuItems(const ShelfID& shelf_id,
                                 const gfx::Point& point,
+                                views::View* source,
                                 ui::MenuSourceType source_type,
                                 std::vector<mojom::MenuItemPtr> menu_items);
 
   // Handles the result of an item selection, records the |action| taken and
   // optionally shows an application menu with the given |menu_items|.
   void AfterItemSelected(
       const ShelfItem& item,
       views::Button* sender,
       std::unique_ptr<ui::Event> event,
       views::InkDrop* ink_drop,
@@ skipping 176 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_