onDownloadData
Called when some part of the response is read. |data| contains the current bytes received since the last call. This method will not be called if the UR_FLAG_NO_DOWNLOAD_DATA flag is set on the request.
Called when some part of the response is read. |data| contains the current bytes received since the last call. This method will not be called if the UR_FLAG_NO_DOWNLOAD_DATA flag is set on the request.