Refactor and push window properties up to class properties.

ui/aura/mus/mus_util.cc

 // Copyright 2015 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/mus/mus_util.h"
 
 #include "ui/aura/window.h"
-#include "ui/aura/window_property.h"
+#include "ui/base/class_property.h"
 
 namespace aura {
 namespace {
 
 // This code uses Set/GetNativeWindowProperty instead of Set/GetProperty to
 // avoid a dependency on mus.
 const char kMusWindowKey[] = "mus";
 
 }  // namespace
 
 ui::Window* GetMusWindow(Window* window) {
   if (!window)
     return nullptr;
   return static_cast<ui::Window*>(
       window->GetNativeWindowProperty(kMusWindowKey));
 }
 
 void SetMusWindow(Window* window, ui::Window* mus_window) {
   window->SetNativeWindowProperty(kMusWindowKey, mus_window);
 }
 
 }  // namespace aura