Refactoring: Add convenience method toPluginContainerImpl.

Source/web/WebHelperPluginImpl.cpp

 /*
  * Copyright (C) 2012 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 148 matching lines @@
 
     RefPtr<NodeList> objectElements = m_page->mainFrame()->document()->getElementsByTagName(WebCore::HTMLNames::objectTag.localName());
     ASSERT(objectElements && objectElements->length() == 1);
     if (!objectElements || objectElements->length() < 1)
         return 0;
     Node* node = objectElements->item(0);
     ASSERT(node->hasTagName(WebCore::HTMLNames::objectTag));
     WebCore::Widget* widget = toHTMLPlugInElement(node)->pluginWidget();
     if (!widget)
         return 0;
-    WebPlugin* plugin = static_cast<WebPluginContainerImpl*>(widget)->plugin();
+    WebPlugin* plugin = toPluginContainerImpl(widget)->plugin();
     ASSERT(plugin);
     // If the plugin is a placeholder, it is not useful to the caller, and it
     // could be replaced at any time. Therefore, do not return it.
     if (plugin->isPlaceholder())
         return 0;
 
     // The plugin was instantiated and will outlive this object.
     return plugin;
 }
 
@@ skipping 61 matching lines @@
     // A WebHelperPluginImpl instance usually has two references.
     //  - One owned by the instance itself. It represents the visible widget.
     //  - One owned by the hosting element. It's released when the hosting
     //    element asks the WebHelperPluginImpl to close.
     // We need them because the closing operation is asynchronous and the widget
     // can be closed while the hosting element is unaware of it.
     return adoptRef(new WebHelperPluginImpl(client)).leakRef();
 }
 
 } // namespace WebKit