Use tighter typing in table rendering code

Source/core/rendering/RenderTableCell.h

Index: Source/core/rendering/RenderTableCell.h
diff --git a/Source/core/rendering/RenderTableCell.h b/Source/core/rendering/RenderTableCell.h
index 0107a54f8875c366b8e1f6e6ecc4717f2b6676e9..689b99bb0e022a4e07afce32fe2b731fbdebed04 100644
--- a/Source/core/rendering/RenderTableCell.h
+++ b/Source/core/rendering/RenderTableCell.h
@@ -4,7 +4,7 @@
  *           (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, 2009 Apple Inc. All rights reserved.
+ * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2009, 2013 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
@@ -77,6 +77,9 @@ public:
     RenderTableSection* section() const { return toRenderTableSection(parent()->parent()); }
     RenderTable* table() const { return toRenderTable(parent()->parent()->parent()); }
 
+    RenderTableCell* previousCell() const;
+    RenderTableCell* nextCell() const;
+
     unsigned rowIndex() const
     {
         // This function shouldn't be called on a detached cell.
@@ -277,6 +280,9 @@ private:
     unsigned parseRowSpanFromDOM() const;
     unsigned parseColSpanFromDOM() const;
 
+    void nextSibling() const WTF_DELETED_FUNCTION;
+    void previousSibling() const WTF_DELETED_FUNCTION;
+
     // Note MSVC will only pack members if they have identical types, hence we use unsigned instead of bool here.
     unsigned m_column : 29;
     unsigned m_cellWidthChanged : 1;
@@ -288,6 +294,28 @@ private:
 
 DEFINE_RENDER_OBJECT_TYPE_CASTS(RenderTableCell, isTableCell());
 
+inline RenderTableCell* RenderTableCell::previousCell() const
+{
+    return toRenderTableCell(RenderObject::previousSibling());
+}
+
+inline RenderTableCell* RenderTableCell::nextCell() const
+{
+    return toRenderTableCell(RenderObject::nextSibling());
+}
+
+inline RenderTableCell* RenderTableRow::firstCell() const
+{
+    ASSERT(children() == virtualChildren());
+    return toRenderTableCell(children()->firstChild());
+}
+
+inline RenderTableCell* RenderTableRow::lastCell() const
+{
+    ASSERT(children() == virtualChildren());
+    return toRenderTableCell(children()->lastChild());
+}
+
 } // namespace WebCore
 
 #endif // RenderTableCell_h