Moves mash/wm into ash/mus

ash/mus/root_windows_observer.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 MASH_WM_ROOT_WINDOW_OBSERVERS_H_
-#define MASH_WM_ROOT_WINDOW_OBSERVERS_H_
+#ifndef ASH_MUS_ROOT_WINDOW_OBSERVERS_H_
+#define ASH_MUS_ROOT_WINDOW_OBSERVERS_H_
 
-namespace mash {
-namespace wm {
+namespace ash {
+namespace mus {
 
 class RootWindowController;
 
 class RootWindowsObserver {
  public:
   // Called once a new display has been created and the root Window obtained.
   virtual void OnRootWindowControllerAdded(
       RootWindowController* controller) = 0;
 
  protected:
   ~RootWindowsObserver() {}
 };
 
-}  // namespace wm
-}  // namespace mash
+}  // namespace mus
+}  // namespace ash
 
-#endif  // MASH_WM_ROOT_WINDOW_OBSERVERS_H_
+#endif  // ASH_MUS_ROOT_WINDOW_OBSERVERS_H_