Reduce forward declarations in core/rendering

Source/core/rendering/RenderRegion.h

 /*
  * Copyright (C) 2011 Adobe Systems Incorporated. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  *
  * 1. Redistributions of source code must retain the above
  *    copyright notice, this list of conditions and the following
  *    disclaimer.
@@ skipping 19 matching lines @@
 #ifndef RenderRegion_h
 #define RenderRegion_h
 
 #include "core/rendering/RenderBlockFlow.h"
 #include "core/rendering/style/StyleInheritedData.h"
 
 namespace WebCore {
 
 struct LayerFragment;
 typedef Vector<LayerFragment, 1> LayerFragments;
-class RenderBox;
 class RenderFlowThread;
 
 class RenderRegion : public RenderBlockFlow {
 public:
     explicit RenderRegion(Element*, RenderFlowThread*);
 
     virtual bool isRenderRegion() const OVERRIDE FINAL { return true; }
 
     void setFlowThreadPortionRect(const LayoutRect& rect) { m_flowThreadPortionRect = rect; }
     LayoutRect flowThreadPortionRect() const { return m_flowThreadPortionRect; }
@@ skipping 60 matching lines @@
 private:
     LayoutRect m_flowThreadPortionRect;
     bool m_isValid : 1;
 };
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderRegion, isRenderRegion());
 
 } // namespace WebCore
 
 #endif // RenderRegion_h