Dart: Better handle leak checks. close() is async.

examples/dart/wget/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.
 
 // Run with, e.g.:
 // mojo_shell "mojo:dart_wget http://www.google.com"
 
 import 'dart:async';
 import 'dart:typed_data';
 import 'dart:mojo.application';
@@ skipping 17 matching lines @@
     if (args == null || args.length != 2) {
       throw "Expected URL argument";
     }
 
     ByteData bodyData = await _getUrl(args[1]);
     print(">>> Body <<<");
     print(new String.fromCharCodes(bodyData.buffer.asUint8List()));
     print(">>> EOF <<<");
 
     _closeProxies();
-    close();
+    await close();
+    assert(MojoHandle.reportLeakedHandles());
   }
 
   Future<ByteData> _getUrl(String url) async {
     _initProxiesIfNeeded();
 
     var urlRequest = new UrlRequest()
-        ..url = url
-        ..autoFollowRedirects = true;
+      ..url = url
+      ..autoFollowRedirects = true;
 
     var urlResponse = await _urlLoader.ptr.start(urlRequest);
     print(">>> Headers <<<");
     print(urlResponse.response.headers.join('\n'));
 
     return DataPipeDrainer.drainHandle(urlResponse.response.body);
   }
 
   void _initProxiesIfNeeded() {
     if (_networkService == null) {
@@ skipping 11 matching lines @@
     _urlLoader = null;
     _networkService.close();
     _networkService = null;
   }
 }
 
 main(List args) {
   MojoHandle appHandle = new MojoHandle(args[0]);
   new WGet.fromHandle(appHandle);
 }