Pass shelf instances, not root windows, for ash context menus.

ash/shelf/shelf_alignment_menu.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_SHELF_SHELF_ALIGNMENT_MENU_H_
 #define ASH_SHELF_SHELF_ALIGNMENT_MENU_H_
 
 #include "ash/ash_export.h"
 #include "base/macros.h"
 #include "ui/base/models/simple_menu_model.h"
 
-namespace aura {
-class RootWindow;
-}
+namespace ash {
 
-namespace ash {
+class Shelf;
 
 // Submenu for choosing the alignment of the launcher.
 class ASH_EXPORT ShelfAlignmentMenu : public ui::SimpleMenuModel,
                                       public ui::SimpleMenuModel::Delegate {
  public:
-  explicit ShelfAlignmentMenu(aura::Window* root);
+  explicit ShelfAlignmentMenu(Shelf* shelf);
   ~ShelfAlignmentMenu() override;
 
   // ui::SimpleMenuModel::Delegate overrides:
   bool IsCommandIdChecked(int command_id) const override;
   bool IsCommandIdEnabled(int command_id) const override;
   bool GetAcceleratorForCommandId(int command_id,
                                   ui::Accelerator* accelerator) override;
   void ExecuteCommand(int command_id, int event_flags) override;
 
  private:
   enum MenuItem {
     // Offset so as not to interfere with other menus.
     MENU_ALIGN_LEFT = 500,
     MENU_ALIGN_RIGHT,
     MENU_ALIGN_BOTTOM,
   };
 
-  aura::Window* root_window_;
+  Shelf* shelf_;
 
   DISALLOW_COPY_AND_ASSIGN(ShelfAlignmentMenu);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SHELF_SHELF_ALIGNMENT_MENU_H_