Avoid calling slower Node::firstChild() / Node::lastChild() when possible

Source/core/dom/NodeTraversal.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * 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
@@ skipping 92 matching lines @@
         descendant = child;
     return descendant;
 }
 
 Node* NodeTraversal::previous(const Node& current, const Node* stayWithin)
 {
     if (current == stayWithin)
         return 0;
     if (current.previousSibling()) {
         Node* previous = current.previousSibling();
-        while (previous->lastChild())
-            previous = previous->lastChild();
+        while (Node* child = previous->lastChild())
+            previous = child;
         return previous;
     }
     return current.parentNode();
 }
 
 Node* NodeTraversal::previousSkippingChildren(const Node& current, const Node* stayWithin)
 {
     if (current == stayWithin)
         return 0;
     if (current.previousSibling())
         return current.previousSibling();
     for (Node* parent = current.parentNode(); parent; parent = parent->parentNode()) {
         if (parent == stayWithin)
             return 0;
         if (parent->previousSibling())
             return parent->previousSibling();
     }
     return 0;
 }
 
 Node* NodeTraversal::nextPostOrder(const Node& current, const Node* stayWithin)
 {
     if (current == stayWithin)
         return 0;
     if (!current.nextSibling())
         return current.parentNode();
     Node* next = current.nextSibling();
-    while (next->firstChild())
-        next = next->firstChild();
+    while (Node* child = next->firstChild())
+        next = child;
     return next;
 }
 
 static Node* previousAncestorSiblingPostOrder(const Node& current, const Node* stayWithin)
 {
     ASSERT(!current.previousSibling());
     for (Node* parent = current.parentNode(); parent; parent = parent->parentNode()) {
         if (parent == stayWithin)
             return 0;
         if (parent->previousSibling())
             return parent->previousSibling();
     }
     return 0;
 }
 
 Node* NodeTraversal::previousPostOrder(const Node& current, const Node* stayWithin)
 {
-    if (current.lastChild())
-        return current.lastChild();
+    if (Node* lastChild = current.lastChild())
+        return lastChild;
     if (current == stayWithin)
         return 0;
     if (current.previousSibling())
         return current.previousSibling();
     return previousAncestorSiblingPostOrder(current, stayWithin);
 }
 
 } // namespace WebCore