Add toHTMLFieldSetElement and toHTMLLegendElement, and use them.

Source/core/html/HTMLFormControlsCollection.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2010, 2011, 2012 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
  * version 2 of the License, or (at your option) any later version.
  *
@@ skipping 39 matching lines @@
 HTMLFormControlsCollection::~HTMLFormControlsCollection()
 {
 }
 
 const Vector<FormAssociatedElement*>& HTMLFormControlsCollection::formControlElements() const
 {
     ASSERT(ownerNode());
     ASSERT(ownerNode()->hasTagName(formTag) || ownerNode()->hasTagName(fieldsetTag));
     if (ownerNode()->hasTagName(formTag))
         return toHTMLFormElement(ownerNode())->associatedElements();
-    return static_cast<HTMLFieldSetElement*>(ownerNode())->associatedElements();
+    return toHTMLFieldSetElement(ownerNode())->associatedElements();
 }
 
 const Vector<HTMLImageElement*>& HTMLFormControlsCollection::formImageElements() const
 {
     ASSERT(ownerNode());
     return toHTMLFormElement(ownerNode())->imageElements();
 }
 
 Element* HTMLFormControlsCollection::virtualItemAfter(unsigned& offset, Element* previousItem) const
 {
@@ skipping 100 matching lines @@
         returnValue1Enabled = true;
         returnValue1 = namedItems.at(0);
         return;
     }
 
     returnValue0Enabled = true;
     returnValue0 = this->ownerNode()->radioNodeList(name);
 }
 
 }