Add toHTMLDialogElement(), and use it.

Source/core/dom/Document.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2006 Alexey Proskuryakov (ap@webkit.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2008, 2009, 2011, 2012 Google Inc. All rights reserved.
  * Copyright (C) 2010 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) Research In Motion Limited 2010-2011. All rights reserved.
@@ skipping 4964 matching lines @@
     size_t position = m_topLayerElements.find(element);
     ASSERT(position != notFound);
     m_topLayerElements.remove(position);
     element->setIsInTopLayer(false);
 }
 
 HTMLDialogElement* Document::activeModalDialog() const
 {
     if (m_topLayerElements.isEmpty())
         return 0;
-    return static_cast<HTMLDialogElement*>(m_topLayerElements.last().get());
+    return toHTMLDialogElement(m_topLayerElements.last().get());
 }
 
 void Document::webkitExitPointerLock()
 {
     if (!page())
         return;
     if (Element* target = page()->pointerLockController().element()) {
         if (&target->document() != this)
             return;
     }
@@ skipping 455 matching lines @@
 {
     return DocumentLifecycleNotifier::create(this);
 }
 
 DocumentLifecycleNotifier* Document::lifecycleNotifier()
 {
     return static_cast<DocumentLifecycleNotifier*>(ScriptExecutionContext::lifecycleNotifier());
 }
 
 } // namespace WebCore