Introduce toHTMLFormControlElement, 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 124 matching lines @@
 }
 
 PassRefPtr<FormSubmission> FormSubmission::create(HTMLFormElement* form, const Attributes& attributes, PassRefPtr<Event> event, FormSubmissionTrigger trigger)
 {
     ASSERT(form);
 
     HTMLFormControlElement* submitButton = 0;
     if (event && event->target()) {
         for (Node* node = event->target()->toNode(); node; node = node->parentNode()) {
             if (node->isElementNode() && toElement(node)->isFormControlElement()) {
-                submitButton = static_cast<HTMLFormControlElement*>(node);
+                submitButton = toHTMLFormControlElement(node);
                 break;
             }
         }
     }
 
     FormSubmission::Attributes copiedAttributes;
     copiedAttributes.copyFrom(attributes);
     if (submitButton) {
         String attributeValue;
         if (!(attributeValue = submitButton->getAttribute(formactionAttr)).isNull())
@@ skipping 88 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);
 }
 
 }