Dart: Futures -> Callbacks.

benchmarks/mojo_rtt_benchmark/lib/echo_server.dart

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 import 'dart:async';
 
 import 'package:mojo/application.dart';
 import 'package:mojo/bindings.dart';
 import 'package:mojo/core.dart';
 import 'package:_mojo_for_test_only/mojo/examples/echo.mojom.dart';
 
 class EchoImpl implements Echo {
   EchoInterface _echo;
   EchoApplication _application;
 
   EchoImpl(this._application, MojoMessagePipeEndpoint endpoint) {
     _echo = new EchoInterface.fromEndpoint(endpoint, this);
     _echo.ctrl.onError = _errorHandler;
   }
 
-  echoString(String value, [Function responseFactory]) =>
-      responseFactory(value);
+  void echoString(String value, void respond(String response)) {
+    respond(value);
+  }
 
   Future close() => _echo.close();
 
   _errorHandler(Object e) => _application.removeService(this);
 }
 
 class EchoApplication extends Application {
   List<EchoImpl> _echoServices;
   bool _closing;
 
@@ skipping 32 matching lines @@
       await service.close();
     }
     MojoHandle.reportLeakedHandles();
   }
 }
 
 main(List args, Object handleToken) {
   MojoHandle appHandle = new MojoHandle(handleToken);
   new EchoApplication.fromHandle(appHandle);
 }