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

Source/core/loader/DocumentLoader.cpp

Index: Source/core/loader/DocumentLoader.cpp
diff --git a/Source/core/loader/DocumentLoader.cpp b/Source/core/loader/DocumentLoader.cpp
index e82b92e8c4206f27da928123704ca1075493f67a..abb7134c095ce4873624fbdcb14be8b8a0ad2476 100644
--- a/Source/core/loader/DocumentLoader.cpp
+++ b/Source/core/loader/DocumentLoader.cpp
@@ -526,7 +526,10 @@ void DocumentLoader::ensureWriter(const AtomicString& mimeType, const KURL& over
     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();