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

third_party/WebKit/Source/web/WebFormElement.cpp

 /*
  * Copyright (C) 2009 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 86 matching lines @@
 void WebFormElement::finishRequestAutocomplete(WebFormElement::AutocompleteResult result)
 {
     unwrap<HTMLFormElement>()->finishRequestAutocomplete(static_cast<HTMLFormElement::AutocompleteResult>(result));
 }
 
 WebFormElement::WebFormElement(const PassRefPtrWillBeRawPtr<HTMLFormElement>& e)
     : WebElement(e)
 {
 }
 
+DEFINE_WEB_NODE_TYPE_CASTS(WebFormElement, isHTMLFormElement(constUnwrap<Node>()));
+
 WebFormElement& WebFormElement::operator=(const PassRefPtrWillBeRawPtr<HTMLFormElement>& e)
 {
     m_private = e;
     return *this;
 }
 
 WebFormElement::operator PassRefPtrWillBeRawPtr<HTMLFormElement>() const
 {
     return toHTMLFormElement(m_private.get());
 }
 
 } // namespace blink