Use tighter typing in table rendering code

Source/core/rendering/RenderTableCell.cpp

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009 Apple 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 723 matching lines @@
     result = chooseBorder(result, CollapsedBorderValue(parent()->style()->borderBefore(), includeColor ? parent()->resolveColor(beforeColorProperty) : Color(), BROW));
     if (!result.exists())
         return result;
 
     // (4) The previous row's after border.
     if (prevCell) {
         RenderObject* prevRow = 0;
         if (prevCell->section() == section())
             prevRow = parent()->previousSibling();
         else
-            prevRow = prevCell->section()->lastChild();
+            prevRow = prevCell->section()->lastRow();
 
         if (prevRow) {
             result = chooseBorder(CollapsedBorderValue(prevRow->style()->borderAfter(), includeColor ? prevRow->resolveColor(afterColorProperty) : Color(), BROW), result);
             if (!result.exists())
                 return result;
         }
     }
 
     // Now check row groups.
     RenderTableSection* currSection = section();
@@ skipping 518 matching lines @@
 
 RenderTableCell* RenderTableCell::createAnonymousWithParentRenderer(const RenderObject* parent)
 {
     RenderTableCell* newCell = RenderTableCell::createAnonymous(&parent->document());
     RefPtr<RenderStyle> newStyle = RenderStyle::createAnonymousStyleWithDisplay(parent->style(), TABLE_CELL);
     newCell->setStyle(newStyle.release());
     return newCell;
 }
 
 } // namespace WebCore