anchor.diff:    Command respond();
   }
   
  +/**
  + * Sample Command usage
  + */
   // TODO(ericarnold): Testing.  Remove.
   class TestMessage extends Command{
     String message;
  
positive.code: 
      Uri workerUri = Uri.parse(workerPath);
  
      Isolate.spawnUri(workerUri, [], receivePort.sendPort);
      return completer.future;
    }
  
    bool isWorker = false;
    ServiceHandler.worker(this.receivePort, this.sendPort) {
      isWorker = true;
      receivePort.listen((command) {
        performCommand(command);
      });
    }
  
    ServiceHandler.owner(this.receivePort);
  
    sendCommand(Command command) {
      sendPort.send({
          "response": false,
          "id": command.commandId,
          "data": command.serialize()});
  
negative.code: import 'dart:async';
  import 'dart:convert';
  
  /**
   * Defines a class which contains services and handles their communication.
   */
  class Services {
    final String _workerPath = 'services/services_isolate.dart';
    ServiceHandler _handler;
    SendPort _sendPort;
    final ReceivePort _receivePort = new ReceivePort();
  
    void ping() {
      TestMessage command = new TestMessage.yell('Marco');
      print("Sending '$command'");
      _handler.sendCommand(command);
    }
  
    Services() {
      _handler = new ServiceHandler.owner(_receivePort);
  
      // TODO(ericarnold): Provide an onReady handler
      _handler.listenForSendPort(_workerPath).then((_){
        ping();
      });
    }
  }
  
  /**
   * Defines a handler for isolates which is unified between worker and origin.
   */
  class ServiceHandler {
    SendPort _sendPort;
    ReceivePort _receivePort;
    bool _isWorker = false;
  
    ServiceHandler.worker(this._receivePort, this._sendPort) {
      _isWorker = true;
      _receivePort.listen((command) {
        performCommand(command);
      });
    }
  
    ServiceHandler.owner(this._receivePort);
  
    Future listenForSendPort(String workerPath) {
      Completer completer = new Completer();
      _receivePort.listen((parameter) {
        if (_sendPort == null) {
          _sendPort = parameter;
          completer.complete();
        } else {
          performCommand(parameter);
  