Use new Traversal<SVG*Element> API more in SVG code

Source/core/svg/SVGFEMergeElement.cpp

 /*
  * Copyright (C) 2004, 2005, 2007 Nikolas Zimmermann <zimmermann@kde.org>
  * Copyright (C) 2004, 2005, 2006 Rob Buis <buis@kde.org>
  *
  * 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.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 26 matching lines @@
 
 PassRefPtr<SVGFEMergeElement> SVGFEMergeElement::create(Document& document)
 {
     return adoptRef(new SVGFEMergeElement(document));
 }
 
 PassRefPtr<FilterEffect> SVGFEMergeElement::build(SVGFilterBuilder* filterBuilder, Filter* filter)
 {
     RefPtr<FilterEffect> effect = FEMerge::create(filter);
     FilterEffectVector& mergeInputs = effect->inputEffects();
-    for (Element* element = ElementTraversal::firstWithin(*this); element; element = ElementTraversal::nextSibling(*element)) {
-        if (element->hasTagName(SVGNames::feMergeNodeTag)) {
-            FilterEffect* mergeEffect = filterBuilder->getEffectById(AtomicString(toSVGFEMergeNodeElement(element)->in1()->currentValue()->value()));
-            if (!mergeEffect)
-                return nullptr;
-            mergeInputs.append(mergeEffect);
-        }
+    for (SVGFEMergeNodeElement* element = Traversal<SVGFEMergeNodeElement>::firstChild(*this); element; element = Traversal<SVGFEMergeNodeElement>::nextSibling(*element)) {
+        FilterEffect* mergeEffect = filterBuilder->getEffectById(AtomicString(element->in1()->currentValue()->value()));
+        if (!mergeEffect)
+            return nullptr;
+        mergeInputs.append(mergeEffect);
     }
 
     if (mergeInputs.isEmpty())
         return nullptr;
 
     return effect.release();
 }
 
 }