Add an experiment group via Settings to tokenize synchronously

third_party/WebKit/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 1007 matching lines @@
 
     if (shouldUseThreading()) {
         double bytesReceivedTime = monotonicallyIncreasingTimeMS();
         if (!m_haveBackgroundParser)
             startBackgroundParser();
 
         std::unique_ptr<Vector<char>> buffer = wrapUnique(new Vector<char>(length));
         memcpy(buffer->data(), data, length);
         TRACE_EVENT1(TRACE_DISABLED_BY_DEFAULT("blink.debug"), "HTMLDocumentParser::appendBytes", "size", (unsigned)length);
 
-        postTaskToLookaheadParser(crossThreadBind(&BackgroundHTMLParser::appendRawBytesFromMainThread, m_backgroundParser, passed(std::move(buffer)), bytesReceivedTime));
+        LookaheadParserTaskSynchrony policy = document()->settings() && document()->settings()->parseHTMLOnMainThreadSyncTokenize() ? Synchronous : Asynchronous;
+        postTaskToLookaheadParser(crossThreadBind(&BackgroundHTMLParser::appendRawBytesFromMainThread, m_backgroundParser, passed(std::move(buffer)), bytesReceivedTime), policy);
         return;
     }
 
     DecodedDataDocumentParser::appendBytes(data, length);
 }
 
 void HTMLDocumentParser::flush()
 {
     // If we've got no decoder, we never received any data.
     if (isDetached() || needsDecoder())
@@ skipping 100 matching lines @@
         (*closure)();
         return;
     case Asynchronous:
         m_loadingTaskRunner->postTask(BLINK_FROM_HERE, std::move(closure));
         return;
     }
     NOTREACHED();
 }
 
 } // namespace blink