Turn DocumentParser::pinToMainThread into a cleaner api

Source/core/xmlhttprequest/XMLHttpRequest.cpp

 /*
  *  Copyright (C) 2004, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005-2007 Alexey Proskuryakov <ap@webkit.org>
  *  Copyright (C) 2007, 2008 Julien Chaffraix <jchaffraix@webkit.org>
  *  Copyright (C) 2008, 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
@@ skipping 1592 matching lines @@
 }
 
 void XMLHttpRequest::parseDocumentChunk(const char* data, unsigned len)
 {
     if (!m_responseDocumentParser) {
         ASSERT(!m_responseDocument);
         initResponseDocument();
         if (!m_responseDocument)
             return;
 
-        m_responseDocumentParser = m_responseDocument->implicitOpen();
+        m_responseDocumentParser = m_responseDocument->implicitOpen(AllowAsynchronousParsing);
         m_responseDocumentParser->addClient(this);
     }
     ASSERT(m_responseDocumentParser);
 
     if (m_responseDocumentParser->needsDecoder())
         m_responseDocumentParser->setDecoder(createDecoder());
 
     m_responseDocumentParser->appendBytes(data, len);
 }
 
@@ skipping 168 matching lines @@
     visitor->trace(m_responseDocument);
     visitor->trace(m_responseDocumentParser);
     visitor->trace(m_progressEventThrottle);
     visitor->trace(m_upload);
     visitor->trace(m_blobLoader);
     XMLHttpRequestEventTarget::trace(visitor);
     DocumentParserClient::trace(visitor);
 }
 
 } // namespace blink