Mandoline UI Process: Update namespaces and file names

components/mus/surfaces/surfaces_state.cc

 // Copyright 2015 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.
 
 #include "components/mus/surfaces/surfaces_state.h"
 
-namespace surfaces {
+namespace mus {
 
 SurfacesState::SurfacesState() : next_id_namespace_(1u) {}
 
 SurfacesState::~SurfacesState() {}
 
-}  // namespace surfaces
+}  // namespace mus