Implement async file API on top of isolates.

tests/standalone/src/DirectoryInvalidArgumentsTest.dart

+// Copyright (c) 2011, 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.
+
 class DirectoryInvalidArgumentsTest {
   static void testFailingList(Directory d, var recursive) {
     int errors = 0;
     d.setErrorHandler((error) {
       errors += 1;
     });
     d.setDoneHandler((completed) {
       Expect.equals(1, errors);
       Expect.isFalse(completed);
     });
@@ skipping 22 matching lines @@
   }
 
   static void testMain() {
     testInvalidArguments();
   }
 }
 
 main() {
   DirectoryInvalidArgumentsTest.testMain();
 }