Dart: Use a RawReceivePort to receive events for Mojo handles.

services/dart/test/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:service_test_interfaces/test/echo_service.mojom.dart';
@@ skipping 31 matching lines @@
       ApplicationConnection connection) {
     connection.provideService(
         EchoServiceName, (endpoint) => new EchoServiceImpl(this, endpoint));
   }
 }
 
 main(List args) {
   MojoHandle appHandle = new MojoHandle(args[0]);
   String url = args[1];
   new EchoApplication.fromHandle(appHandle)
-    ..onError = (() {
+    ..onError = ((_) {
       MojoHandle.reportLeakedHandles();
     });
 }