showProgressBar() {
    if (this.progressBar_ || this.showProcessingTimeout_) {
      return;
    }
    this.showProcessingTimeout_ = window.setTimeout(() => {
      this.disposeCurrentComponent_();
      this.progressBar_ = new Spinner();
      this.currentComponent_ = this.progressBar_;
      this.progressBar_.render(this.container_);
      this.showProcessingTimeout_ = null;
    }, SHOW_PROCESSING_DELAY);
  }
Renders progress bar in the container if hidden.
@override