Implement aura::PropertyConverter for mus interop.

ui/aura/window.h

 // 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.
 
 #ifndef UI_AURA_WINDOW_H_
 #define UI_AURA_WINDOW_H_
 
 #include <stdint.h>
 
 #include <map>
@@ skipping 329 matching lines @@
   // Returns true if there was state needing to be cleaned up.
   bool CleanupGestureState();
 
  protected:
   // Deletes (or removes if not owned by parent) all child windows. Intended for
   // use from the destructor.
   void RemoveOrDestroyChildren();
 
  private:
   friend class LayoutManager;
+  friend class PropertyConverter;
   friend class WindowPort;
   friend class WindowTargeter;
   friend class subtle::PropertyHelper;
   friend class test::WindowTestApi;
 
   // Called by the public {Set,Get,Clear}Property functions.
   int64_t SetPropertyInternal(const void* key,
                               const char* name,
                               PropertyDeallocator deallocator,
                               int64_t value,
@@ skipping 173 matching lines @@
   };
 
   std::map<const void*, Value> prop_map_;
 
   DISALLOW_COPY_AND_ASSIGN(Window);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_H_