constructor(type, options = {}) {
    super(type);

    this[kData] = options.data === undefined ? null : options.data;
  }
Create a new `MessageEvent`.

@param {String} type The name of the event
@param {Object} [options] A dictionary object that allows for setting
    attributes via object members of the same name
@param {*} [options.data=null] The message content