// TODO(ussuri): this could be bound in the HTML via
// `@observable SparkPolymer app` initialized to [spark].
// But [spark] is initialized asynchronously and that happens to be later
// than any of the events associated with this object. Find a way to do
// that.
void onMenuSelected(CustomEvent event, Map<String, dynamic> detail) =>
    spark.onMenuSelected(event, detail);