Use ContainerNode::hasChildren() instead of firstChild() in conditionals

Source/core/dom/TreeWalker.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2000 Frederik Holljen (frederik.holljen@hig.no)
  * Copyright (C) 2001 Peter Kelly (pmk@post.com)
  * Copyright (C) 2006 Samuel Weinig (sam.weinig@gmail.com)
  * Copyright (C) 2004, 2008 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
@@ skipping 64 matching lines @@
 {
     for (RefPtrWillBeRawPtr<Node> node = m_current->firstChild(); node; ) {
         short acceptNodeResult = acceptNode(node.get(), exceptionState);
         if (exceptionState.hadException())
             return 0;
         switch (acceptNodeResult) {
             case NodeFilter::FILTER_ACCEPT:
                 m_current = node.release();
                 return m_current.get();
             case NodeFilter::FILTER_SKIP:
-                if (node->firstChild()) {
+                if (node->hasChildren()) {
                     node = node->firstChild();
                     continue;
                 }
                 break;
             case NodeFilter::FILTER_REJECT:
                 break;
         }
         do {
             if (node->nextSibling()) {
                 node = node->nextSibling();
@@ skipping 86 matching lines @@
     while (1) {
         for (RefPtrWillBeRawPtr<Node> sibling = node->nextSibling(); sibling; ) {
             short acceptNodeResult = acceptNode(sibling.get(), exceptionState);
             if (exceptionState.hadException())
                 return 0;
             switch (acceptNodeResult) {
                 case NodeFilter::FILTER_ACCEPT:
                     m_current = sibling.release();
                     return m_current.get();
                 case NodeFilter::FILTER_SKIP:
-                    if (sibling->firstChild()) {
+                    if (sibling->hasChildren()) {
                         sibling = sibling->firstChild();
                         node = sibling;
                         continue;
                     }
                     break;
                 case NodeFilter::FILTER_REJECT:
                     break;
             }
             sibling = sibling->nextSibling();
         }
@@ skipping 74 matching lines @@
     return 0;
 }
 
 void TreeWalker::trace(Visitor* visitor)
 {
     visitor->trace(m_current);
     NodeIteratorBase::trace(visitor);
 }
 
 } // namespace blink