Use template specialization to generate WindowProperty code

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 <map>
 #include <string>
 #include <vector>
@@ skipping 34 matching lines @@
 
 class LayoutManager;
 class WindowDelegate;
 class WindowObserver;
 class WindowTreeHost;
 
 // Defined in window_property.h (which we do not include)
 template<typename T>
 struct WindowProperty;
 
+namespace subtle {
+class PropertyHelper;
+}
+
 namespace test {
 class WindowTestApi;
 }
 
 // Aura window implementation. Interesting events are sent to the
 // WindowDelegate.
 // TODO(beng): resolve ownership.
 class AURA_EXPORT Window : public ui::LayerDelegate,
                            public ui::LayerOwner,
                            public ui::EventTarget,
@@ skipping 260 matching lines @@
 
  protected:
   // Deletes (or removes if not owned by parent) all child windows. Intended for
   // use from the destructor.
   void RemoveOrDestroyChildren();
 
  private:
   friend class test::WindowTestApi;
   friend class LayoutManager;
   friend class WindowTargeter;
-
+  friend class subtle::PropertyHelper;
   // Called by the public {Set,Get,Clear}Property functions.
   int64 SetPropertyInternal(const void* key,
                             const char* name,
                             PropertyDeallocator deallocator,
                             int64 value,
                             int64 default_value);
   int64 GetPropertyInternal(const void* key, int64 default_value) const;
 
   // Returns true if the mouse pointer at relative-to-this-Window's-origin
   // |local_point| can trigger an event for this Window.
@@ skipping 191 matching lines @@
   };
 
   std::map<const void*, Value> prop_map_;
 
   DISALLOW_COPY_AND_ASSIGN(Window);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_H_