[XHR] Reduce 'readystatechange' event firing.

Source/core/xml/XMLHttpRequest.h

 /*
  *  Copyright (C) 2003, 2006, 2008 Apple Inc. All rights reserved.
  *  Copyright (C) 2005, 2006 Alexey Proskuryakov <ap@nypop.com>
  *  Copyright (C) 2011 Google Inc. All rights reserved.
  *  Copyright (C) 2012 Intel Corporation
  *
  *  This library is free software; you can redistribute it and/or
  *  modify it under the terms of the GNU Lesser General Public
  *  License as published by the Free Software Foundation; either
  *  version 2 of the License, or (at your option) any later version.
@@ skipping 230 matching lines @@
     // notification is received from m_loader and thrown at the end of send() if
     // any.
     ExceptionCode m_exceptionCode;
 
     XMLHttpRequestProgressEventThrottle m_progressEventThrottle;
 
     // An enum corresponding to the allowed string values for the responseType attribute.
     ResponseTypeCode m_responseTypeCode;
     RefPtr<SecurityOrigin> m_securityOrigin;
 
+    double m_previousReadyStateChangeFireTime;
+
     bool m_async;
     bool m_includeCredentials;
     // Used to skip m_responseDocument creation if it's done previously. We need
     // this separate flag since m_responseDocument can be 0 for some cases.
     bool m_createdDocument;
     bool m_error;
     bool m_uploadEventsAllowed;
     bool m_uploadComplete;
     bool m_sameOriginRequest;
 };
 
 } // namespace blink
 
 #endif // XMLHttpRequest_h