ash: Cleanup class/struct forward declarations

ash/system/chromeos/screen_layout_observer.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 ASH_SYSTEM_CHROMEOS_SCREEN_LAYOUT_OBSERVER_H_
 #define ASH_SYSTEM_CHROMEOS_SCREEN_LAYOUT_OBSERVER_H_
 
 #include <stdint.h>
 
 #include <map>
 
 #include "ash/ash_export.h"
 #include "ash/common/wm_display_observer.h"
 #include "base/macros.h"
 #include "base/strings/string16.h"
 #include "ui/display/manager/managed_display_info.h"
 
 namespace ash {
 
-class DisplayView;
-
 // ScreenLayoutObserver is responsible to send notification to users when screen
 // resolution changes or screen rotation changes.
 class ASH_EXPORT ScreenLayoutObserver : public WmDisplayObserver {
  public:
   ScreenLayoutObserver();
   ~ScreenLayoutObserver() override;
 
   // Overridden from WmDisplayObserver:
   void OnDisplayConfigurationChanged() override;
 
@@ skipping 31 matching lines @@
   DisplayInfoMap display_info_;
 
   bool show_notifications_for_testing = true;
 
   DISALLOW_COPY_AND_ASSIGN(ScreenLayoutObserver);
 };
 
 }  // namespace ash
 
 #endif  // ASH_SYSTEM_CHROMEOS_SCREEN_LAYOUT_OBSERVER_H_