Clean up forward declarations in core/rendering and core/painting

Source/core/paint/VideoPainter.h

 // Copyright 2014 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 VideoPainter_h
 #define VideoPainter_h
 
 namespace blink {
 
-class GraphicsContext;
 struct PaintInfo;
 class LayoutPoint;
-class LayoutRect;
 class RenderVideo;
 
 class VideoPainter {
 public:
     VideoPainter(RenderVideo& renderVideo) : m_renderVideo(renderVideo) { }
 
     void paintReplaced(PaintInfo&, const LayoutPoint&);
 
 private:
 
     RenderVideo& m_renderVideo;
 };
 
 } // namespace blink
 
 #endif // VideoPainter_h