Consistently use ElementTraversal API when looking for an Element

Source/core/html/track/LoadableTextTrack.cpp

 /*
  * Copyright (C) 2011 Google Inc.  All rights reserved.
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  * modification, are permitted provided that the following conditions
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  * PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR
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 #include "config.h"
 #include "core/html/track/LoadableTextTrack.h"
 
+#include "core/dom/ElementTraversal.h"
 #include "core/html/HTMLTrackElement.h"
 #include "core/html/track/TextTrackCueList.h"
 #include "core/html/track/vtt/VTTRegionList.h"
 
 namespace WebCore {
 
 using namespace HTMLNames;
 
 LoadableTextTrack::LoadableTextTrack(HTMLTrackElement* track)
     : TextTrack(track->document(), track, emptyAtom, emptyAtom, emptyAtom, emptyAtom, TrackElement)
@@ skipping 97 matching lines @@
         regions()->add(newRegions[i]);
     }
 }
 
 size_t LoadableTextTrack::trackElementIndex()
 {
     ASSERT(m_trackElement);
     ASSERT(m_trackElement->parentNode());
 
     size_t index = 0;
-    for (Node* node = m_trackElement->parentNode()->firstChild(); node; node = node->nextSibling()) {
-        if (!node->hasTagName(trackTag) || !node->parentNode())
+    for (Element* child = ElementTraversal::firstWithin(*m_trackElement->parentNode()); child; child = ElementTraversal::nextSibling(*child)) {
+        if (!child->hasTagName(trackTag) || !child->parentNode())
             continue;
-        if (node == m_trackElement)
+        if (child == m_trackElement)
             return index;
         ++index;
     }
     ASSERT_NOT_REACHED();
 
     return 0;
 }
 
 } // namespace WebCore