mash: remove more shell/shelf WmWindow usage.

ash/scoped_root_window_for_new_windows.cc

 // 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.
 
 #include "ash/scoped_root_window_for_new_windows.h"
 
 #include "ash/shell.h"
 #include "base/logging.h"
 
 namespace ash {
 
 ScopedRootWindowForNewWindows::ScopedRootWindowForNewWindows(
-    WmWindow* new_root) {
+    aura::Window* new_root) {
   DCHECK(new_root);
   Shell::Get()->scoped_root_window_for_new_windows_ = new_root;
 }
 
 ScopedRootWindowForNewWindows::~ScopedRootWindowForNewWindows() {
   Shell::Get()->scoped_root_window_for_new_windows_ = nullptr;
 }
 
 }  // namespace ash