Make XHR use the background HTML parser

Source/core/html/parser/HTMLDocumentParser.cpp

 /*
  * Copyright (C) 2010 Google, Inc. All Rights Reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 726 matching lines @@
 {
     ASSERT(!isStopped());
     ASSERT(shouldUseThreading());
     ASSERT(!m_haveBackgroundParser);
     m_haveBackgroundParser = true;
 
     RefPtr<WeakReference<BackgroundHTMLParser> > reference = WeakReference<BackgroundHTMLParser>::createUnbound();
     m_backgroundParser = WeakPtr<BackgroundHTMLParser>(reference);
 
     // TODO(oysteine): Disabled due to crbug.com/398076 until a full fix can be implemented.
-    if (RuntimeEnabledFeatures::threadedParserDataReceiverEnabled())
-        document()->loader()->attachThreadedDataReceiver(adoptPtr(new ParserDataReceiver(m_backgroundParser)));
+    if (RuntimeEnabledFeatures::threadedParserDataReceiverEnabled()) {
+        if (DocumentLoader* loader = document()->loader())
+            loader->attachThreadedDataReceiver(adoptPtr(new ParserDataReceiver(m_backgroundParser)));
+    }
 
     OwnPtr<BackgroundHTMLParser::Configuration> config = adoptPtr(new BackgroundHTMLParser::Configuration);
     config->options = m_options;
     config->parser = m_weakFactory.createWeakPtr();
     config->xssAuditor = adoptPtr(new XSSAuditor);
     config->xssAuditor->init(document(), &m_xssAuditorDelegate);
     config->preloadScanner = adoptPtr(new TokenPreloadScanner(document()->url().copy(), createMediaValues(document())));
     config->decoder = takeDecoder();
 
     ASSERT(config->xssAuditor->isSafeToSendToAnotherThread());
@@ skipping 313 matching lines @@
 void HTMLDocumentParser::setDecoder(PassOwnPtr<TextResourceDecoder> decoder)
 {
     ASSERT(decoder);
     DecodedDataDocumentParser::setDecoder(decoder);
 
     if (m_haveBackgroundParser)
         HTMLParserThread::shared()->postTask(bind(&BackgroundHTMLParser::setDecoder, m_backgroundParser, takeDecoder()));
 }
 
 }