Makes ash/mus use RootWindowControllerCommon

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 55 matching lines @@
 }
 
 // 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,
                            public ui::GestureConsumer {
  public:
+  // Initial value of id() for newly created windows.
+  static constexpr int kInitialId = -1;
+
   // Used when stacking windows.
   enum StackDirection {
     STACK_ABOVE,
     STACK_BELOW
   };
 
   typedef std::vector<Window*> Windows;
 
   explicit Window(WindowDelegate* delegate);
   ~Window() override;
@@ skipping 434 matching lines @@
   };
 
   std::map<const void*, Value> prop_map_;
 
   DISALLOW_COPY_AND_ASSIGN(Window);
 };
 
 }  // namespace aura
 
 #endif  // UI_AURA_WINDOW_H_