code: function addExpect100Continue(req) {
      var len = req.httpRequest.headers['Content-Length'];
      if (AWS.util.isNode() && (len >= 1024 * 1024 || req.params.Body instanceof AWS.util.stream.Stream)) {
        req.httpRequest.headers['Expect'] = '100-continue';
      }
    }
docs: Adds Expect: 100-continue header if payload is greater-or-equal 1MB
  @api private