Introduce toHTMLInputElement(Node*), and use it.

Source/core/loader/FormSubmission.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 168 matching lines @@
     WTF::TextEncoding dataEncoding = isMailtoForm ? UTF8Encoding() : FormDataBuilder::encodingFromAcceptCharset(copiedAttributes.acceptCharset(), document);
     RefPtr<DOMFormData> domFormData = DOMFormData::create(dataEncoding.encodingForFormSubmission());
     Vector<pair<String, String> > formValues;
 
     bool containsPasswordData = false;
     for (unsigned i = 0; i < form->associatedElements().size(); ++i) {
         FormAssociatedElement* control = form->associatedElements()[i];
         HTMLElement* element = toHTMLElement(control);
         if (!element->isDisabledFormControl())
             control->appendFormData(*domFormData, isMultiPartForm);
-        if (element->hasLocalName(inputTag)) {
-            HTMLInputElement* input = static_cast<HTMLInputElement*>(control);
+        if (element->hasTagName(inputTag)) {
+            HTMLInputElement* input = toHTMLInputElement(element);
             if (input->isTextField())
                 formValues.append(pair<String, String>(input->name().string(), input->value()));
             if (input->isPasswordField() && !input->value().isEmpty())
                 containsPasswordData = true;
         }
     }
 
     RefPtr<FormData> formData;
     String boundary;
 
@@ skipping 43 matching lines @@
             frameRequest.resourceRequest().setHTTPContentType(m_contentType);
         else
             frameRequest.resourceRequest().setHTTPContentType(m_contentType + "; boundary=" + m_boundary);
     }
 
     frameRequest.resourceRequest().setURL(requestURL());
     FrameLoader::addHTTPOriginIfNeeded(frameRequest.resourceRequest(), m_origin);
 }
 
 }