chromeos: Fix chrome --mus startup crashes on device

components/exo/wm_helper_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 COMPONENTS_EXO_WM_HELPER_MUS_H_
 #define COMPONENTS_EXO_WM_HELPER_MUS_H_
 
 #include "base/macros.h"
 #include "components/exo/wm_helper.h"
 #include "ui/aura/client/focus_change_observer.h"
 #include "ui/aura/mus/focus_synchronizer_observer.h"
 #include "ui/events/devices/input_device_event_observer.h"
 
 namespace aura {
 namespace client {
 class ActivationClient;
 }
 }
 
 namespace exo {
 
 // A helper class for accessing WindowManager related features.
+// This is only used for mash. Mushrome uses WMHelperAsh.
 class WMHelperMus : public WMHelper,
                     public ui::InputDeviceEventObserver,
                     public aura::FocusSynchronizerObserver,
                     public aura::client::FocusChangeObserver {
  public:
   WMHelperMus();
   ~WMHelperMus() override;
 
   // Overridden from WMHelper:
   const display::ManagedDisplayInfo GetDisplayInfo(
@@ skipping 36 matching lines @@
   aura::Window* root_with_active_focus_client_ = nullptr;
   aura::Window* active_window_ = nullptr;
   aura::Window* focused_window_ = nullptr;
 
   DISALLOW_COPY_AND_ASSIGN(WMHelperMus);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_WM_HELPER_H_