Cleanup: Add conversion interface for WebWidget derived classes.

Source/web/ChromeClientImpl.cpp

 /*
  * Copyright (C) 2009 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies).
  *
  * 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.
@@ skipping 697 matching lines @@
         getPopupMenuInfo(popupContainer, &popupInfo);
         webwidget = m_webView->client()->createPopupMenu(popupInfo);
     } else {
         webwidget = m_webView->client()->createPopupMenu(
             convertPopupType(popupContainer->popupType()));
         // We only notify when the WebView has to handle the popup, as when
         // the popup is handled externally, the fact that a popup is showing is
         // transparent to the WebView.
         m_webView->popupOpened(popupContainer);
     }
-    static_cast<WebPopupMenuImpl*>(webwidget)->initialize(popupContainer, bounds);
+    toWebPopupMenuImpl(webwidget)->initialize(popupContainer, bounds);
 }
 
 void ChromeClientImpl::popupClosed(WebCore::PopupContainer* popupContainer)
 {
     m_webView->popupClosed(popupContainer);
 }
 
 void ChromeClientImpl::setCursor(const WebCore::Cursor& cursor)
 {
     setCursor(WebCursorInfo(cursor));
@@ skipping 278 matching lines @@
 {
 }
 
 void NavigatorContentUtilsClientImpl::registerProtocolHandler(const String& scheme, const String& baseURL, const String& url, const String& title)
 {
     m_webView->client()->registerProtocolHandler(scheme, baseURL, url, title);
 }
 #endif
 
 } // namespace WebKit