Fix const correctness of containerForRepaint

Source/core/rendering/RenderFrameSet.cpp

 /**
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Simon Hausmann <hausmann@kde.org>
  *           (C) 2000 Stefan Schimanski (1Stein@gmx.de)
  * Copyright (C) 2004, 2005, 2006 Apple Computer, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 423 matching lines @@
 
     return result;
 }
 
 void RenderFrameSet::layout()
 {
     ASSERT(needsLayout());
 
     bool doFullRepaint = selfNeedsLayout() && checkForRepaintDuringLayout();
     LayoutRect oldBounds;
-    RenderLayerModelObject* repaintContainer = 0;
+    const RenderLayerModelObject* repaintContainer = 0;
     if (doFullRepaint) {
         repaintContainer = containerForRepaint();
         oldBounds = clippedOverflowRectForRepaint(repaintContainer);
     }
 
     if (!parent()->isFrameSet() && !document().printing()) {
         setWidth(view()->viewWidth());
         setHeight(view()->viewHeight());
     }
 
@@ skipping 206 matching lines @@
         return SetCursor;
     }
     if (canResizeColumn(roundedPoint)) {
         cursor = columnResizeCursor();
         return SetCursor;
     }
     return RenderBox::getCursor(point, cursor);
 }
 
 } // namespace WebCore