delete useThreading flag as it is always true

Source/core/html/parser/HTMLDocumentParser.h

 /*
  * 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 150 matching lines @@
     void constructTreeFromCompactHTMLToken(const CompactHTMLToken&);
 
     void runScriptsForPausedTreeBuilder();
     void resumeParsingAfterScriptExecution();
 
     void attemptToEnd();
     void endIfDelayed();
     void attemptToRunDeferredScriptsAndEnd();
     void end();
 
-    bool shouldUseThreading() const { return m_options.useThreading && !m_isPinnedToMainThread; }
+    bool shouldUseThreading() const { return !m_isPinnedToMainThread; }
 
     bool isParsingFragment() const;
     bool isScheduledForResume() const;
     bool inPumpSession() const { return m_pumpSessionNestingLevel > 0; }
     bool shouldDelayEnd() const { return inPumpSession() || isWaitingForScripts() || isScheduledForResume() || isExecutingScript(); }
 
     HTMLToken& token() { return *m_token; }
 
     HTMLParserOptions m_options;
     HTMLInputStream m_input;
@@ skipping 20 matching lines @@
 
     bool m_isPinnedToMainThread;
     bool m_endWasDelayed;
     bool m_haveBackgroundParser;
     unsigned m_pumpSessionNestingLevel;
 };
 
 }
 
 #endif