anchor.diff:      }
     }
   
  -  handleCommand(Command command, bool isResponse) {
  +  void handleCommand(Command command, bool isResponse) {
       if (isResponse) {
  -      // TODO(ericarnold): Complete a future
  +      // TODO(ericarnold): Complete a future (returned by sendCommand)/
         print("response: " + command.toString());
       } else {
         sendResponse(command);
       }
     }
   
  -  sendResponse(Command command) {
  +  void sendResponse(Command command) {
       Command responseObject = command.respond();
  -    sendPort.send({
  +    _sendPort.send({
           "response": true,
           "id": responseObject.commandId,
           "data": responseObject.serialize()});
     }
   }
   
  +/**
  + * Defines an abstract class whose interface is identical at the origin and the
  + * worker, but which provides functionality only on the responder and acts as a
  + * simple proxy on the other end.
  + */
   abstract class Command {
     Command();
     Command.serialized(String serializedData);
  
positive.code:   Command respond();
  }
  
  // TODO(ericarnold): Testing.  Remove.
  class TestMessage extends Command{
    String message;
  
negative.code: 
      Uri workerUri = Uri.parse(workerPath);
  
      Isolate.spawnUri(workerUri, [], _receivePort.sendPort);
      return completer.future;
    }
  
    Future sendCommand(Command command) {
      _sendPort.send({
          "response": false,
          "id": command.commandId,
          "data": command.serialize()});
  