components: Cleanup class/struct fwd declarations

components/exo/keyboard.h

 // 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.
 
 #ifndef COMPONENTS_EXO_KEYBOARD_H_
 #define COMPONENTS_EXO_KEYBOARD_H_
 
 #include <vector>
 
 #include "base/macros.h"
 #include "components/exo/surface_observer.h"
 #include "components/exo/wm_helper.h"
 #include "ui/aura/client/focus_change_observer.h"
 #include "ui/events/event_handler.h"
 
 namespace ui {
 enum class DomCode;
-class Event;
 class KeyEvent;
 }
 
 namespace exo {
 class KeyboardDelegate;
 class Surface;
 
 // This class implements a client keyboard that represents one or more keyboard
 // devices.
 class Keyboard : public ui::EventHandler,
@@ skipping 28 matching lines @@
 
   // Current set of modifier flags.
   int modifier_flags_ = 0;
 
   DISALLOW_COPY_AND_ASSIGN(Keyboard);
 };
 
 }  // namespace exo
 
 #endif  // COMPONENTS_EXO_KEYBOARD_H_