Make aura work with mus

ui/aura/mus/mus_types.h

-// Copyright 2014 The Chromium Authors. All rights reserved.
+// 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 SERVICES_UI_COMMON_TYPES_H_
-#define SERVICES_UI_COMMON_TYPES_H_
+#ifndef UI_AURA_MUS_MUS_TYPES_H_
+#define UI_AURA_MUS_MUS_TYPES_H_
 
 #include <stdint.h>
 
 // Typedefs for the transport types. These typedefs match that of the mojom
 // file, see it for specifics.
 
-namespace ui {
+namespace aura {
 
 // Used to identify windows and change ids.
-typedef uint32_t Id;
+using Id = uint32_t;
 
 // Used to identify a client as well as a client-specific window id. For
 // example, the Id for a window consists of the ClientSpecificId of the client
 // and the ClientSpecificId of the window.
-typedef uint16_t ClientSpecificId;
+using ClientSpecificId = uint16_t;
+
+constexpr Id kInvalidServerId = 0;
 
 }  // namespace ui
 
-#endif  // SERVICES_UI_COMMON_TYPES_H_
+#endif  // UI_AURA_MUS_MUS_TYPES_H_