Add a test that we resume commits after inserting the body.

Source/core/loader/DocumentLoader.cpp

 /*
  * Copyright (C) 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2011 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.
@@ skipping 508 matching lines @@
 
     const AtomicString& encoding = m_frame->host()->overrideEncoding().isNull() ? response().textEncodingName() : m_frame->host()->overrideEncoding();
 
     // Prepare a DocumentInit before clearing the frame, because it may need to
     // inherit an aliased security context.
     DocumentInit init(url(), m_frame);
     init.withNewRegistrationContext();
     m_frame->loader().clear();
     ASSERT(m_frame->page());
 
-    ParserSynchronizationPolicy parsingPolicy = (m_substituteData.isValid() && m_substituteData.forceSynchronousLoad()) ? ForceSynchronousParsing : AllowAsynchronousParsing;
+    ParserSynchronizationPolicy parsingPolicy = AllowAsynchronousParsing;
+    if ((m_substituteData.isValid() && m_substituteData.forceSynchronousLoad()) || !Document::threadedParsingEnabledForUnitTestsOnly())
+        parsingPolicy = ForceSynchronousParsing;
+
     m_writer = createWriterFor(0, init, mimeType, encoding, false, parsingPolicy);
     m_writer->setDocumentWasLoadedAsPartOfNavigation();
 
     // This should be set before receivedFirstData().
     if (!overridingURL.isEmpty())
         m_frame->document()->setBaseURLOverride(overridingURL);
 
     // Call receivedFirstData() exactly once per load.
     frameLoader()->receivedFirstData();
     m_frame->document()->maybeHandleHttpRefresh(m_response.httpHeaderField("Refresh"), Document::HttpRefreshFromHeader);
@@ skipping 322 matching lines @@
 {
     m_writer = createWriterFor(ownerDocument, init, mimeType(), m_writer ? m_writer->encoding() : emptyAtom, true, ForceSynchronousParsing);
     if (!source.isNull())
         m_writer->appendReplacingData(source);
     endWriting(m_writer.get());
 }
 
 DEFINE_WEAK_IDENTIFIER_MAP(DocumentLoader);
 
 } // namespace blink