Cleanup remaining class/struct fwd declarations

headless/lib/browser/headless_screen.h

 // Copyright 2016 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 HEADLESS_LIB_BROWSER_HEADLESS_SCREEN_H_
 #define HEADLESS_LIB_BROWSER_HEADLESS_SCREEN_H_
 
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "ui/aura/window_observer.h"
 #include "ui/display/display.h"
 #include "ui/display/screen_base.h"
 
 namespace gfx {
 class Insets;
 class Rect;
 class Transform;
 }
 
 namespace aura {
 class Window;
-class WindowParentingClient;
 class WindowTreeHost;
 }
 
 namespace headless {
 
 class HeadlessScreen : public display::ScreenBase, public aura::WindowObserver {
  public:
   // Creates a display::Screen of the specified size (physical pixels).
   static HeadlessScreen* Create(const gfx::Size& size);
   ~HeadlessScreen() override;
@@ skipping 26 matching lines @@
 
   aura::WindowTreeHost* host_;
   float ui_scale_;
 
   DISALLOW_COPY_AND_ASSIGN(HeadlessScreen);
 };
 
 }  // namespace headless
 
 #endif  // HEADLESS_LIB_BROWSER_HEADLESS_SCREEN_H_