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

mojo/dart/test/validation_test.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 'dart:convert';
 import 'dart:isolate';
 import 'dart:typed_data';
 import 'mojo:bindings';
 import 'mojo:builtin' as builtin;
@@ skipping 18 matching lines @@
   method2(StructB param0, StructA param1) => _complete();
   method3(List<bool> param0) => _complete();
   method4(StructC param0, List<int> param1) => _complete();
   method5(StructE param0, MojoDataPipeProducer param1) => _complete();
   method6(List<List<int>> param0) => _complete();
   method7(StructF param0, List<List<int>> param1) => _complete();
   method8(List<List<String>> param0) => _complete();
   method9(List<List<MojoHandle>> param0) => _complete();
   method10(Map<String, int> param0) => _complete();
 
-  void close({bool nodefer: false}) => _stub.close(nodefer: nodefer);
+  Future close({bool nodefer: false}) => _stub.close(nodefer: nodefer);
 }
 
 parser.ValidationParseResult readAndParseTest(String test) {
   List<int> data = builtin.readSync("${test}.data");
   String input = new Utf8Decoder().convert(data).trim();
   return parser.parse(input);
 }
 
 String expectedResult(String test) {
   List<int> data = builtin.readSync("${test}.expected");
@@ skipping 45 matching lines @@
 
   // First test the parser.
   parser.parserTests();
 
   // Then run the conformance tests.
   getTestFiles(path, "$path/conformance_").forEach((test) {
     runTest(test, readAndParseTest(test), expectedResult(test));
   });
   // TODO(zra): Add integration tests when they no longer rely on Client=.
 }