Gracefully handle XMLDocumentParser being detached by mutation events.

Source/core/xml/parser/XMLDocumentParser.h

 /*
  * Copyright (C) 2000 Peter Kelly (pmk@post.com)
  * Copyright (C) 2005, 2006, 2007 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Samuel Weinig (sam@webkit.org)
  * Copyright (C) 2008 Nokia Corporation and/or its subsidiary(-ies)
  * Copyright (C) 2008, 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
  * License as published by the Free Software Foundation; either
@@ skipping 131 matching lines @@
 
 private:
     void initializeParserContext(const CString& chunk = CString());
 
     void pushCurrentNode(ContainerNode*);
     void popCurrentNode();
     void clearCurrentNodeStack();
 
     void insertErrorMessageBlock();
 
-    void enterText();
-    void exitText();
+    void createLeafTextNodeIfNeeded();
+    bool updateLeafTextNode();
 
     void doWrite(const String&);
     void doEnd();
 
     bool m_hasView;
 
     SegmentedString m_originalSourceForTransform;
 
     xmlParserCtxtPtr context() const { return m_context ? m_context->context() : 0; }
     RefPtr<XMLParserContext> m_context;
@@ skipping 28 matching lines @@
     PrefixForNamespaceMap m_prefixToNamespaceMap;
     SegmentedString m_pendingSrc;
 };
 
 xmlDocPtr xmlDocPtrForString(Document*, const String& source, const String& url);
 HashMap<String, String> parseAttributes(const String&, bool& attrsOK);
 
 } // namespace blink
 
 #endif // XMLDocumentParser_h