ui: Cleanup class/struct forward declarations

ui/views/widget/desktop_aura/x11_whole_screen_move_loop.h

 // Copyright (c) 2013 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_X11_WHOLE_SCREEN_MOVE_LOOP_H_
 #define UI_VIEWS_WIDGET_DESKTOP_AURA_X11_WHOLE_SCREEN_MOVE_LOOP_H_
 
 #include <stdint.h>
 
 #include "base/callback.h"
@@ skipping 14 matching lines @@
 }
 
 namespace ui {
 class MouseEvent;
 class ScopedEventDispatcher;
 class XScopedEventSelector;
 }
 
 namespace views {
 
-class Widget;
-
 // Runs a nested message loop and grabs the mouse. This is used to implement
 // dragging.
 class X11WholeScreenMoveLoop : public X11MoveLoop,
                                public ui::PlatformEventDispatcher {
  public:
   explicit X11WholeScreenMoveLoop(X11MoveLoopDelegate* delegate);
   ~X11WholeScreenMoveLoop() override;
 
   // ui:::PlatformEventDispatcher:
   bool CanDispatchEvent(const ui::PlatformEvent& event) override;
@@ skipping 47 matching lines @@
 
   std::unique_ptr<ui::MouseEvent> last_motion_in_screen_;
   base::WeakPtrFactory<X11WholeScreenMoveLoop> weak_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(X11WholeScreenMoveLoop);
 };
 
 }  // namespace views
 
 #endif  // UI_VIEWS_WIDGET_DESKTOP_AURA_X11_WHOLE_SCREEN_MOVE_LOOP_H_