ash: Cleanup class/struct forward declarations

ash/common/system/tray/tray_bubble_wrapper.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_COMMON_SYSTEM_TRAY_TRAY_BUBBLE_WRAPPER_H_
 #define ASH_COMMON_SYSTEM_TRAY_TRAY_BUBBLE_WRAPPER_H_
 
 #include "base/macros.h"
 #include "ui/views/widget/widget_observer.h"
 
 namespace views {
 class TrayBubbleView;
 }
 
 namespace ash {
 class TrayBackgroundView;
-class TrayEventFilter;
 
 // Creates and manages the Widget and EventFilter components of a bubble.
 
 class TrayBubbleWrapper : public views::WidgetObserver {
  public:
   TrayBubbleWrapper(TrayBackgroundView* tray,
                     views::TrayBubbleView* bubble_view);
   ~TrayBubbleWrapper() override;
 
   // views::WidgetObserver overrides:
@@ skipping 12 matching lines @@
   TrayBackgroundView* tray_;
   views::TrayBubbleView* bubble_view_;  // unowned
   views::Widget* bubble_widget_;
 
   DISALLOW_COPY_AND_ASSIGN(TrayBubbleWrapper);
 };
 
 }  // namespace ash
 
 #endif  // ASH_COMMON_SYSTEM_TRAY_TRAY_BUBBLE_WRAPPER_H_