Use new Traversal<> API more in the code base

Source/core/html/HTMLLabelElement.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, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.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 19 matching lines @@
 #include "core/dom/ElementTraversal.h"
 #include "core/editing/FrameSelection.h"
 #include "core/events/MouseEvent.h"
 #include "core/frame/LocalFrame.h"
 #include "core/html/FormAssociatedElement.h"
 
 namespace blink {
 
 using namespace HTMLNames;
 
-static bool supportsLabels(const Element& element)
-{
-    if (!element.isHTMLElement())
-        return false;
-    if (!toHTMLElement(element).isLabelable())
-        return false;
-    return toLabelableElement(element).supportLabels();
-}
-
 inline HTMLLabelElement::HTMLLabelElement(Document& document)
     : HTMLElement(labelTag, document)
 {
     ScriptWrappable::init(this);
 }
 
 DEFINE_NODE_FACTORY(HTMLLabelElement)
 
 bool HTMLLabelElement::rendererIsFocusable() const
 {
     HTMLLabelElement* that = const_cast<HTMLLabelElement*>(this);
     return that->isContentEditable();
 }
 
 LabelableElement* HTMLLabelElement::control() const
 {
     const AtomicString& controlId = getAttribute(forAttr);
     if (controlId.isNull()) {
         // Search the children and descendants of the label element for a form element.
         // per http://dev.w3.org/html5/spec/Overview.html#the-label-element
         // the form element must be "labelable form-associated element".
-        for (Element* element = ElementTraversal::next(*this, this); element; element = ElementTraversal::next(*element, this)) {
-            if (!supportsLabels(*element))
-                continue;
-            return toLabelableElement(element);
+        for (LabelableElement* element = Traversal<LabelableElement>::next(*this, this); element; element = Traversal<LabelableElement>::next(*element, this)) {
+            if (element->supportLabels())
+                return element;
         }
         return 0;
     }
 
     if (Element* element = treeScope().getElementById(controlId)) {
-        if (supportsLabels(*element))
+        if (isLabelableElement(*element) && toLabelableElement(*element).supportLabels())
             return toLabelableElement(element);
     }
 
     return 0;
 }
 
 HTMLFormElement* HTMLLabelElement::formOwner() const
 {
     return FormAssociatedElement::findAssociatedForm(this);
 }
@@ skipping 149 matching lines @@
 {
     if (insertionPoint->isInTreeScope() && treeScope() == document()) {
         TreeScope& treeScope = insertionPoint->treeScope();
         if (treeScope.shouldCacheLabelsByForAttribute())
             updateLabel(treeScope, fastGetAttribute(forAttr), nullAtom);
     }
     HTMLElement::removedFrom(insertionPoint);
 }
 
 } // namespace