Fix crash due to unexpected Node deletion during MutationObserver registration book-keeping

Source/core/dom/Node.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 2260 matching lines @@
     Vector<OwnPtr<MutationObserverRegistration> >* registry = mutationObserverRegistry();
     ASSERT(registry);
     if (!registry)
         return;
 
     size_t index = registry->find(registration);
     ASSERT(index != notFound);
     if (index == notFound)
         return;
 
+    // Deleting the registration may cause this node to be derefed, so we must make sure the Vector operation completes
+    // before that, in case |this| is destroyed (see MutationObserverRegistration::m_registrationNodeKeepAlive).
+    // FIXME: Simplify the registration/transient registration logic to make this understandable by humans.
+    RefPtr<Node> protect(this);
     registry->remove(index);
 }
 
 void Node::registerTransientMutationObserver(MutationObserverRegistration* registration)
 {
     ensureRareData()->ensureMutationObserverData()->transientRegistry.add(registration);
 }
 
 void Node::unregisterTransientMutationObserver(MutationObserverRegistration* registration)
 {
@@ skipping 431 matching lines @@
         node->showTreeForThis();
 }
 
 void showNodePath(const WebCore::Node* node)
 {
     if (node)
         node->showNodePathForThis();
 }
 
 #endif