old_contents: var FastBootHeaders = require('./fastboot-headers');
  
  function FastbootResponse(response) {
    this.headers = new FastBootHeaders(response._headers);
    this.statusCode = 200;
  }
  
  module.exports = FastbootResponse;
  
new_contents: 'use strict';
  
  var FastBootHeaders = require('./fastboot-headers');
  
  class FastbootResponse {
    constructor(response) {
      this.headers = new FastBootHeaders(response._headers);
      this.statusCode = 200;
    }
  }
  
  module.exports = FastbootResponse;
  
subject: convert FastbootResponse to es6 class