Refactor and push window properties up to class properties.

ui/aura/mus/window_port_mus.h

Index: ui/aura/mus/window_port_mus.h
diff --git a/ui/aura/mus/window_port_mus.h b/ui/aura/mus/window_port_mus.h
index c293b849c5a8fa5b49c6fe53d8893b0740abbfad..c3018a3682fa698189405595ab5c3579a87ec814 100644
--- a/ui/aura/mus/window_port_mus.h
+++ b/ui/aura/mus/window_port_mus.h
@@ -231,10 +231,10 @@ class AURA_EXPORT WindowPortMus : public WindowPort, public WindowMus {
   void OnVisibilityChanged(bool visible) override;
   void OnDidChangeBounds(const gfx::Rect& old_bounds,
                          const gfx::Rect& new_bounds) override;
-  std::unique_ptr<WindowPortPropertyData> OnWillChangeProperty(
+  std::unique_ptr<ui::PropertyData> OnWillChangeProperty(
       const void* key) override;
   void OnPropertyChanged(const void* key,
-                         std::unique_ptr<WindowPortPropertyData> data) override;
+                         std::unique_ptr<ui::PropertyData> data) override;
 
   WindowTreeClient* window_tree_client_;