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

ash/mus/shell_delegate_mus.h

 // Copyright 2016 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_MUS_SHELL_DELEGATE_MUS_H_
 #define ASH_MUS_SHELL_DELEGATE_MUS_H_
 
 #include <string>
 
 #include "ash/shell_delegate.h"
@@ skipping 28 matching lines @@
   void RemoveVirtualKeyboardStateObserver(
       VirtualKeyboardStateObserver* observer) override;
   app_list::AppListViewDelegate* GetAppListViewDelegate() override;
   ShelfDelegate* CreateShelfDelegate(ShelfModel* model) override;
   ash::SystemTrayDelegate* CreateSystemTrayDelegate() override;
   ash::UserWallpaperDelegate* CreateUserWallpaperDelegate() override;
   ash::SessionStateDelegate* CreateSessionStateDelegate() override;
   ash::AccessibilityDelegate* CreateAccessibilityDelegate() override;
   ash::NewWindowDelegate* CreateNewWindowDelegate() override;
   ash::MediaDelegate* CreateMediaDelegate() override;
-  ui::MenuModel* CreateContextMenu(aura::Window* root_window,
+  ui::MenuModel* CreateContextMenu(ash::Shelf* shelf,
                                    const ash::ShelfItem* item) override;
   GPUSupport* CreateGPUSupport() override;
   base::string16 GetProductName() const override;
   gfx::Image GetDeprecatedAcceleratorImage() const override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ShellDelegateMus);
 };
 
 }  // namespace sysui
 }  // namespace ash
 
 #endif  // ASH_MUS_SHELL_DELEGATE_MUS_H_