Document::shutdown(): remove unnecessary static_cast<>.

third_party/WebKit/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.
@@ skipping 2469 matching lines @@
       for (Node& node : NodeTraversal::descendantsOf(*this)) {
         cache->remove(&node);
       }
     }
   }
 
   styleEngine().didDetach();
 
   frameHost()->eventHandlerRegistry().documentDetached(*this);
 
-  // Since |Document| class has multiple |LifecycleNotifier| as base class,
-  // we need to have |static_cast<SynchronousMutationNotifier>| here.
-  static_cast<SynchronousMutationNotifier*>(this)->notifyContextDestroyed();
+  // Signal destruction to mutation observers.
+  SynchronousMutationNotifier::notifyContextDestroyed();
   m_frame->selection().documentDetached(*this);
 
   // If this Document is associated with a live DocumentLoader, the
   // DocumentLoader will take care of clearing the FetchContext. Deferring
   // to the DocumentLoader when possible also prevents prematurely clearing
   // the context in the case where multiple Documents end up associated with
   // a single DocumentLoader (e.g., navigating to a javascript: url).
   if (!loader())
     m_fetcher->clearContext();
   // If this document is the master for an HTMLImportsController, sever that
@@ skipping 4014 matching lines @@
 }
 
 void showLiveDocumentInstances() {
   WeakDocumentSet& set = liveDocumentSet();
   fprintf(stderr, "There are %u documents currently alive:\n", set.size());
   for (Document* document : set)
     fprintf(stderr, "- Document %p URL: %s\n", document,
             document->url().getString().utf8().data());
 }
 #endif