class NetworkSummaryComponent implements NgShadowRootAware {
  @NgCallback('callback')
  Function callback;

  void onShadowRoot(ShadowRoot shadowRoot) {
    ...
    chart.callMethod('listen', ['line-click', (ev) {
        var name = ev.callMethod('getLineName');
        print(name);
        callback({'name': name});
    }]);
  }
}

<network-summary
    ...
    callback="ctrl.lineClicked">
</network-summary>

<network-summary
    ...
    callback="ctrl.lineClicked(name)">
</network-summary>