add 'slow' prefix to RenderObject's firstChild() / lastChild() methods

Source/core/rendering/RenderBox.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2006, 2007 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
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 737 matching lines @@
     return toRenderBox(nextSibling());
 }
 
 inline RenderBox* RenderBox::parentBox() const
 {
     return toRenderBox(parent());
 }
 
 inline RenderBox* RenderBox::firstChildBox() const
 {
-    return toRenderBox(firstChild());
+    return toRenderBox(slowFirstChild());
 }
 
 inline RenderBox* RenderBox::lastChildBox() const
 {
-    return toRenderBox(lastChild());
+    return toRenderBox(slowLastChild());
 }
 
 inline void RenderBox::setInlineBoxWrapper(InlineBox* boxWrapper)
 {
     if (boxWrapper) {
         ASSERT(!inlineBoxWrapper());
         // m_inlineBoxWrapper should already be 0. Deleting it is a safeguard against security issues.
         // Otherwise, there will two line box wrappers keeping the reference to this renderer, and
         // only one will be notified when the renderer is getting destroyed. The second line box wrapper
         // will keep a stale reference.
         if (UNLIKELY(inlineBoxWrapper() != 0))
             deleteLineBoxWrapper();
     }
 
     ensureRareData().m_inlineBoxWrapper = boxWrapper;
 }
 
 } // namespace WebCore
 
 #endif // RenderBox_h