mash: remove more shell/shelf WmWindow usage.

ash/shell/window_watcher.cc

 // 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.
 
 #include "ash/shell/window_watcher.h"
 
 #include <utility>
 
 #include "ash/public/cpp/shelf_item.h"
 #include "ash/public/cpp/shell_window_ids.h"
@@ skipping 117 matching lines @@
       int index = model->ItemIndexByID(i->first);
       DCHECK_NE(-1, index);
       model->RemoveItemAt(index);
       id_to_window_.erase(i);
       break;
     }
   }
 }
 
 void WindowWatcher::OnDisplayAdded(const display::Display& new_display) {
-  WmWindow* root =
+  aura::Window* root =
       ShellPort::Get()->GetRootWindowForDisplayId(new_display.id());
-  workspace_window_watcher_->RootWindowAdded(root->aura_window());
+  workspace_window_watcher_->RootWindowAdded(root);
 }
 
 void WindowWatcher::OnDisplayRemoved(const display::Display& old_display) {
   // All windows in the display has already been removed, so no need to
   // remove observers.
 }
 
 void WindowWatcher::OnDisplayMetricsChanged(const display::Display&, uint32_t) {
 }
 
 }  // namespace shell
 }  // namespace ash