addSecondarySource(uri, mimeType) {
    if (!this.video_ || !window.ManagedMediaSource || !this.mediaSource_) {
      shaka.log.warning(
          'Secondary source is used only with ManagedMediaSource');
      return;
    }
    if (!this.config_.useSourceElements) {
      return;
    }
    if (this.secondarySource_) {
      this.video_.removeChild(this.secondarySource_);
    }
    this.secondarySource_ = shaka.util.Dom.createSourceElement(uri, mimeType);
    this.video_.appendChild(this.secondarySource_);
    this.video_.disableRemotePlayback = false;
  }
@param {string} uri
@param {string} mimeType