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

Source/core/paint/ScrollbarPainter.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 ScrollbarPainter_h
 #define ScrollbarPainter_h
 
 #include "platform/scroll/Scrollbar.h"
 
 namespace blink {
 
 class GraphicsContext;
-struct PaintInfo;
 class IntRect;
 class LayoutPoint;
 class LayoutRect;
 class RenderScrollbar;
 class RenderScrollbarPart;
 
 class ScrollbarPainter {
 public:
     ScrollbarPainter(RenderScrollbar& renderScrollbar) : m_renderScrollbar(renderScrollbar) { }
 
     void paintPart(GraphicsContext*, ScrollbarPart, const IntRect&);
     static void paintIntoRect(RenderScrollbarPart*, GraphicsContext*, const LayoutPoint& paintOffset, const LayoutRect&);
 
 private:
     RenderScrollbar& m_renderScrollbar;
 };
 
 } // namespace blink
 
 #endif // ScrollbarPainter_h