postMessage method
Post a WebMessage to the entangled port.
Implementation
Future<void> postMessage(WebMessage message) async {
Map<String, dynamic> args = <String, dynamic>{};
args.putIfAbsent('index', () => this._index);
args.putIfAbsent('message', () => message.toMap());
await _webMessageChannel._channel.invokeMethod('postMessage', args);
}