Make WebNode::to<Type>() (and toConst) casts contain type asserts.

third_party/WebKit/Source/web/WebLabelElement.cpp

 /*
  * Copyright (C) 2010 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 30 matching lines @@
 WebElement WebLabelElement::correspondingControl()
 {
     return WebElement(unwrap<HTMLLabelElement>()->control());
 }
 
 WebLabelElement::WebLabelElement(const PassRefPtrWillBeRawPtr<HTMLLabelElement>& elem)
     : WebElement(elem)
 {
 }
 
+DEFINE_WEB_NODE_TYPE_CASTS(WebLabelElement, isHTMLLabelElement(constUnwrap<Node>()));
+
 WebLabelElement& WebLabelElement::operator=(const PassRefPtrWillBeRawPtr<HTMLLabelElement>& elem)
 {
     m_private = elem;
     return *this;
 }
 
 WebLabelElement::operator PassRefPtrWillBeRawPtr<HTMLLabelElement>() const
 {
     return toHTMLLabelElement(m_private.get());
 }
 
 } // namespace blink