Add the beginning of a simple window manager that we'll support on Windows.

ui/aura/mus/window_port_mus.h

 // 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.
 
 #ifndef UI_AURA_MUS_WINDOW_PORT_MUS_H_
 #define UI_AURA_MUS_WINDOW_PORT_MUS_H_
 
 #include <stdint.h>
 
 #include <string>
@@ skipping 220 matching lines @@
   void OnPropertyChanged(const void* key,
                          std::unique_ptr<WindowPortPropertyData> data) override;
 
   WindowTreeClient* window_tree_client_;
 
   Window* window_ = nullptr;
 
   ServerChangeIdType next_server_change_id_ = 0;
   ServerChanges server_changes_;
 
-  SurfaceIdHandler* surface_id_handler_;
+  SurfaceIdHandler* surface_id_handler_ = nullptr;
   std::unique_ptr<SurfaceInfo> surface_info_;
 
   ui::mojom::Cursor predefined_cursor_ = ui::mojom::Cursor::CURSOR_NULL;
 
   DISALLOW_COPY_AND_ASSIGN(WindowPortMus);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_MUS_WINDOW_PORT_MUS_H_