Support Dart 1.8.0.

lib/src/loader.dart

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library unittest.loader;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
 import 'package:path/path.dart' as p;
 
 import 'dart.dart';
+import 'io.dart';
 import 'isolate_test.dart';
 import 'load_exception.dart';
 import 'remote_exception.dart';
 import 'suite.dart';
 
 /// A class for finding test files and loading them into a runnable form.
 class Loader {
   /// The package root to use for loading tests, or `null` to use the automatic
   /// root.
   final String _packageRoot;
@@ skipping 74 matching lines @@
 
   /// Closes the loader and releases all resources allocated by it.
   Future close() {
     for (var isolate in _isolates) {
       isolate.kill();
     }
     _isolates.clear();
     return new Future.value();
   }
 }