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

third_party/WebKit/public/web/WebPluginDocument.h

 /*
  * 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 21 matching lines @@
 #define WebPluginDocument_h
 
 #include "WebDocument.h"
 
 namespace blink {
 
 class PluginDocument;
 class WebPlugin;
 
 // Wraps a WebDocument for full page plugins.
-class WebPluginDocument : public WebDocument {
+class WebPluginDocument final : public WebDocument {
 public:
     WebPluginDocument() { }
     WebPluginDocument(const WebPluginDocument& e) : WebDocument(e) { }
 
     WebPluginDocument& operator=(const WebPluginDocument& e)
     {
         WebNode::assign(e);
         return *this;
     }
     void assign(const WebPluginDocument& d) { WebNode::assign(d); }
 
     BLINK_EXPORT WebPlugin* plugin();
 
 #if BLINK_IMPLEMENTATION
     WebPluginDocument(const PassRefPtrWillBeRawPtr<PluginDocument>&);
     WebPluginDocument& operator=(const PassRefPtrWillBeRawPtr<PluginDocument>&);
     operator PassRefPtrWillBeRawPtr<PluginDocument>() const;
 #endif
 };
 
+DECLARE_WEB_NODE_TYPE_CASTS(WebPluginDocument);
+
 } // namespace blink
 
 #endif