GridPainter::paintChild should take RenderBox reference

Source/core/paint/GridPainter.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 GridPainter_h
 #define GridPainter_h
 
 namespace blink {
 
 struct PaintInfo;
 class LayoutPoint;
 class RenderBox;
 class RenderGrid;
 
 class GridPainter {
 public:
     GridPainter(RenderGrid& renderGrid) : m_renderGrid(renderGrid) { }
 
     void paintChildren(PaintInfo&, const LayoutPoint&);
-    void paintChild(RenderBox*, PaintInfo&, const LayoutPoint&);
+    void paintChild(RenderBox&, PaintInfo&, const LayoutPoint&);
 
     void paint(PaintInfo&, const LayoutPoint& paintOffset);
 
 private:
     RenderGrid& m_renderGrid;
 };
 
 } // namespace blink
 
 #endif // GridPainter_h