Fix const correctness of containerForRepaint

Source/core/rendering/LayoutRepainter.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  *           (C) 2004 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 26 matching lines @@
 public:
     LayoutRepainter(RenderObject&, bool checkForRepaint);
 
     bool checkForRepaint() const { return m_checkForRepaint; }
 
     // Return true if it repainted.
     bool repaintAfterLayout();
 
 private:
     RenderObject& m_object;
-    RenderLayerModelObject* m_repaintContainer;
+    const RenderLayerModelObject* m_repaintContainer;
     // We store these values as LayoutRects, but the final invalidations will be pixel snapped
     LayoutRect m_oldBounds;
     LayoutPoint m_oldOffset;
     bool m_checkForRepaint;
 };
 
 } // namespace WebCore
 
 #endif // LayoutRepainter_h