Update dart:io tests to use asyncStart/asyncEnd

tests/standalone/io/file_write_as_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.
 
-import "package:expect/expect.dart";
 import 'dart:async';
 import 'dart:io';
-import 'dart:isolate';
+
+import "package:async_helper/async_helper.dart";
+import "package:expect/expect.dart";
 
 testWriteAsBytesSync(dir) {
   var f = new File('${dir.path}/bytes_sync.txt');
   var data = [50,50,50];
   f.writeAsBytesSync(data);
   Expect.listEquals(data, f.readAsBytesSync());
   f.writeAsBytesSync(data, mode: FileMode.APPEND);
   var expected = [50, 50, 50, 50, 50, 50];
   Expect.listEquals(expected, f.readAsBytesSync());
 }
@@ skipping 42 matching lines @@
           Expect.equals('$data$data', str);
           completer.complete(true);
         });
       });
     });
   });
   return completer.future;
 }
 
 main() {
-  var port = new ReceivePort();
+  asyncStart();
   var tempDir = new Directory('').createTempSync();
   testWriteAsBytesSync(tempDir);
   testWriteAsStringSync(tempDir);
   testWriteAsBytes(tempDir).then((_) {
     return testWriteAsString(tempDir);
   }).then((_) {
     tempDir.deleteSync(recursive: true);
-    port.close();
+    asyncEnd();
   });
 }