Refactoring: Add convenience method toPluginContainerImpl.

Source/web/WebPluginDocument.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 30 matching lines @@
 using namespace WebCore;
 
 namespace WebKit {
 
 
 WebPlugin* WebPluginDocument::plugin()
 {
     if (!isPluginDocument())
         return 0;
     PluginDocument* doc = unwrap<PluginDocument>();
-    WebPluginContainerImpl* container = static_cast<WebPluginContainerImpl*>(static_cast<PluginDocument*>(doc)->pluginWidget());
+    WebPluginContainerImpl* container = toPluginContainerImpl(static_cast<PluginDocument*>(doc)->pluginWidget());
     return container->plugin();
 }
 
 
 WebPluginDocument::WebPluginDocument(const PassRefPtr<PluginDocument>& elem)
     : WebDocument(elem)
 {
 }
 
 WebPluginDocument& WebPluginDocument::operator=(const PassRefPtr<PluginDocument>& elem)
 {
     m_private = elem;
     return *this;
 }
 
 WebPluginDocument::operator PassRefPtr<PluginDocument>() const
 {
     return static_cast<PluginDocument*>(m_private.get());
 }
 
 } // namespace WebKit