Use new Traversal<*Element> API in svg code for clarity

Source/core/svg/SVGSVGElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2006 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2010 Rob Buis <buis@kde.org>
  * Copyright (C) 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2014 Google, Inc.
  *
  * 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 12 matching lines @@
 #include "config.h"
 
 #include "core/svg/SVGSVGElement.h"
 
 #include "HTMLNames.h"
 #include "SVGNames.h"
 #include "bindings/v8/ScriptEventListener.h"
 #include "core/css/CSSHelper.h"
 #include "core/dom/Document.h"
 #include "core/dom/ElementTraversal.h"
-#include "core/dom/NodeTraversal.h"
 #include "core/dom/StaticNodeList.h"
 #include "core/editing/FrameSelection.h"
 #include "core/events/EventListener.h"
 #include "core/events/ThreadLocalEventNames.h"
 #include "core/frame/LocalFrame.h"
 #include "core/page/FrameTree.h"
 #include "core/frame/FrameView.h"
 #include "core/frame/UseCounter.h"
 #include "core/rendering/RenderObject.h"
 #include "core/rendering/RenderPart.h"
@@ skipping 774 matching lines @@
 // getElementById on SVGSVGElement is restricted to only the child subtree defined by the <svg> element.
 // See http://www.w3.org/TR/SVG11/struct.html#InterfaceSVGSVGElement
 Element* SVGSVGElement::getElementById(const AtomicString& id) const
 {
     Element* element = treeScope().getElementById(id);
     if (element && element->isDescendantOf(this))
         return element;
 
     // Fall back to traversing our subtree. Duplicate ids are allowed, the first found will
     // be returned.
-    for (Node* node = firstChild(); node; node = NodeTraversal::next(*node, this)) {
-        if (!node->isElementNode())
-            continue;
-
-        Element* element = toElement(node);
+    for (Element* element = ElementTraversal::firstWithin(*this); element; element = ElementTraversal::next(*element, this)) {
         if (element->getIdAttribute() == id)
             return element;
     }
     return 0;
 }
 
 }