Adds DesktopWindowTreeHostMus

ui/views/widget/desktop_aura/desktop_window_tree_host_chromeos.cc

-// Copyright 2013 The Chromium Authors. All rights reserved.
+// 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.
 
-#include "ui/aura/window_tree_host.h"
+#include "ui/views/widget/desktop_aura/desktop_window_tree_host.h"
+
 #include "ui/native_theme/native_theme_aura.h"
-#include "ui/views/widget/desktop_aura/desktop_factory_ozone.h"
-#include "ui/views/widget/desktop_aura/desktop_window_tree_host.h"
 
 namespace views {
 
+// static
 DesktopWindowTreeHost* DesktopWindowTreeHost::Create(
     internal::NativeWidgetDelegate* native_widget_delegate,
     DesktopNativeWidgetAura* desktop_native_widget_aura) {
-  DesktopFactoryOzone* d_factory = DesktopFactoryOzone::GetInstance();
-
-  return d_factory->CreateWindowTreeHost(native_widget_delegate,
-                                         desktop_native_widget_aura);
+  // DesktopNativeWidgetAura is only used with mus, and MusClient injects the
+  // DesktopWindowTreeHost so that this is never called.
+  NOTREACHED();
+  return nullptr;
 }
 
 // static
 ui::NativeTheme* DesktopWindowTreeHost::GetNativeTheme(aura::Window* window) {
   return ui::NativeThemeAura::instance();
 }
 
 }  // namespace views