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

third_party/WebKit/public/web/WebTextAreaElement.h

 /*
  * Copyright (C) 2013 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 20 matching lines @@
 #ifndef WebTextAreaElement_h
 #define WebTextAreaElement_h
 
 #include "WebFormControlElement.h"
 
 namespace blink {
 
 class HTMLTextAreaElement;
 
 // Provides access to some properties of a DOM textarea element node.
-class WebTextAreaElement : public WebFormControlElement {
+class WebTextAreaElement final : public WebFormControlElement {
 public:
     WebTextAreaElement() : WebFormControlElement() { }
     WebTextAreaElement(const WebTextAreaElement& element) : WebFormControlElement(element) { }
 
     WebTextAreaElement& operator=(const WebTextAreaElement& element)
     {
         WebFormControlElement::assign(element);
         return *this;
     }
     void assign(const WebTextAreaElement& element) { WebFormControlElement::assign(element); }
 
 #if BLINK_IMPLEMENTATION
     WebTextAreaElement(const PassRefPtrWillBeRawPtr<HTMLTextAreaElement>&);
     WebTextAreaElement& operator=(const PassRefPtrWillBeRawPtr<HTMLTextAreaElement>&);
     operator PassRefPtrWillBeRawPtr<HTMLTextAreaElement>() const;
 #endif
 };
 
+DECLARE_WEB_NODE_TYPE_CASTS(WebTextAreaElement);
+
 } // namespace blink
 
 #endif