play(time) {
    if (typeof time !== 'number') {
      time = this.time;
    }

    this.time = time;

    if (!this.interval_ && typeof time === 'number' && time > 0) {
      this.interval_ = setInterval(this.ws_.goNext.bind(this.ws_), time);
    }
  }
Starts autosliding all the slides if it's not currently doing it and the
autoslide option was a number greater than 0.
@param {?number=} time Amount of milliseconds to wait to go to next slide
automatically.