Dart: Wait to handle events on a Stub until it makes sense to do it.

mojo/dart/apptests/test_apps/pingpong_target/lib/main.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';
 
@@ skipping 18 matching lines @@
   }
 
   void ping(int pingValue) => _pingPongClient.ptr.pong(pingValue + 1);
 
   // These methods are unimplemented; they merely throw on invocation.
   dynamic pingTargetUrl(String url, int count, [Function responseFactory]) =>
       throw "Unimplemented";
   dynamic pingTargetService(
       Object service, int count, [Function responseFactory]) =>
       throw "Unimplemented";
+  dynamic getPingPongServiceDelayed(
+      Object service, [Function responseFactory]) =>
+      throw "Unimplemented";
+
   void getPingPongService(Object service) {
     new PingPongServiceImpl.fromStub(service);
   }
 
   void quit() {}
 }
 
 class PingPongApplication extends Application {
   PingPongApplication.fromHandle(MojoHandle handle) : super.fromHandle(handle);
 
@@ skipping 11 matching lines @@
   Future closeApplication() async {
     await close();
     MojoHandle.reportLeakedHandles();
   }
 }
 
 main(List args, Object handleToken) {
   MojoHandle appHandle = new MojoHandle(handleToken);
   new PingPongApplication.fromHandle(appHandle);
 }