ui: Cleanup class/struct forward declarations

ui/views/widget/desktop_aura/desktop_window_tree_host_x11.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 UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_
 
 #include <stddef.h>
 #include <stdint.h>
 #include <X11/extensions/shape.h>
@@ skipping 22 matching lines @@
 
 namespace ui {
 class EventHandler;
 class XScopedEventSelector;
 }
 
 namespace views {
 class DesktopDragDropClientAuraX11;
 class DesktopWindowTreeHostObserverX11;
 class X11DesktopWindowMoveClient;
-class X11WindowEventFilter;
 
 class VIEWS_EXPORT DesktopWindowTreeHostX11
     : public DesktopWindowTreeHost,
       public aura::WindowTreeHost,
       public ui::PlatformEventDispatcher {
  public:
   DesktopWindowTreeHostX11(
       internal::NativeWidgetDelegate* native_widget_delegate,
       DesktopNativeWidgetAura* desktop_native_widget_aura);
   ~DesktopWindowTreeHostX11() override;
@@ skipping 373 matching lines @@
 
   base::WeakPtrFactory<DesktopWindowTreeHostX11> close_widget_factory_;
   base::WeakPtrFactory<DesktopWindowTreeHostX11> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(DesktopWindowTreeHostX11);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_DESKTOP_WINDOW_TREE_HOST_X11_H_