open(method:string, url:string, async:true, user:any, password:any) {
    log.verbose('XMLHttpRequest open ', method, url, async, user, password)
    this._method = method
    this._url = url
    this._headers = {}
    this._increment = URIUtil.isJSONStreamURI(this._url)
    this._url = this._url.replace(/^JSONStream\:\/\//, '')
    this._dispatchReadStateChange(XMLHttpRequest.OPENED)
  }
XMLHttpRequest.open, always async, user and password not supported. When
this method invoked, headers should becomes empty again.
@param  {string} method Request method
@param  {string} url Request URL
@param  {true} async Always async
@param  {any} user NOT SUPPORTED
@param  {any} password NOT SUPPORTED