Work around issue 9252 in scheduled_test.

pkg/scheduled_test/test/descriptor_test.dart

 // Copyright (c) 2013, 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 descriptor_test;
 
 import 'dart:async';
 import 'dart:io';
 
 import '../../../pkg/pathos/lib/path.dart' as path;
@@ skipping 893 matching lines @@
       sandbox = dir.path;
       d.defaultRoot = sandbox;
     });
   });
 
   currentSchedule.onComplete.schedule(() {
     d.defaultRoot = null;
     if (sandbox == null) return;
     var oldSandbox = sandbox;
     sandbox = null;
-    return new Directory(oldSandbox).delete(recursive: true);
+    return deleteDir(oldSandbox);
   });
 }
 
 Future<List<int>> byteStreamToList(Stream<List<int>> stream) {
   return stream.reduce(<int>[], (buffer, chunk) {
     buffer.addAll(chunk);
     return buffer;
   });
 }
 
 Future<String> byteStreamToString(Stream<List<int>> stream) =>
   byteStreamToList(stream).then((bytes) => new String.fromCharCodes(bytes));