getIdentifierFromAsset_(asset) {
    // Custom assets can't have special characters like [ or ] in their name,
    // and none of the default assets will have that in their name, so we can
    // be sure that no asset will have [CUSTOM] in its name.
    return asset.name +
           (asset.source == shakaAssets.Source.CUSTOM ? ' [CUSTOM]' : '');
  }
Gets a unique storage identifier for an asset.
@param {!ShakaDemoAssetInfo} asset
@return {string}
@private