Dart: Futures -> Callbacks.

mojo/dart/apptests/test_apps/echo/lib/main.dart

 // Copyright 2014 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/test/echo_service.mojom.dart';
 
 class EchoServiceImpl implements EchoService {
   EchoServiceInterface _service;
   Application _application;
 
   EchoServiceImpl(this._application, MojoMessagePipeEndpoint endpoint) {
     _service = new EchoServiceInterface.fromEndpoint(endpoint, this);
   }
 
-  dynamic echoString(String value, [Function responseFactory]) {
+  void echoString(String value, void callback(String value)) {
     if (value == "quit") {
       _service.close();
     }
-    return responseFactory(value);
+    callback(value);
   }
 
-  dynamic delayedEchoString(String value, int millis,
-      [Function responseFactory]) {
+  void delayedEchoString(
+      String value, int millis, void callback(String value)) {
     if (value == "quit") {
       _service.close();
     }
-    return new Future.delayed(
-        new Duration(milliseconds: millis), () => responseFactory(value));
+    new Future.delayed(
+        new Duration(milliseconds: millis), () => callback(value));
   }
 
   void swap() {
     _swapImpls(this);
   }
 
   void quit() {}
 
   static void _swapImpls(EchoServiceImpl impl) {
     final stub = impl._service;
@@ skipping 18 matching lines @@
   }
 }
 
 main(List args, Object handleToken) {
   MojoHandle appHandle = new MojoHandle(handleToken);
   new EchoApplication.fromHandle(appHandle)
     ..onError = ((_) {
       MojoHandle.reportLeakedHandles();
     });
 }