Modify tests to use Directory.systemTemp

tests/standalone/io/file_output_stream_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.
 // Testing file input stream, VM-only, standalone test.
 
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 void testOpenOutputStreamSync() {
-  Directory tempDirectory = new Directory('').createTempSync();
+  Directory tempDirectory =
+      Directory.systemTemp.createTempSync('dart_file_output_stream');
 
   asyncStart();
   String fileName = "${tempDirectory.path}/test";
   File file = new File(fileName);
   file.createSync();
   IOSink x = file.openWrite();
   var data = [65, 66, 67];
   x.add(data);
   x.close();
   x.done.then((_) {
     Expect.listEquals(file.readAsBytesSync(), data);
     file.deleteSync();
     tempDirectory.deleteSync();
     asyncEnd();
   });
 }
 
 
 main() {
   testOpenOutputStreamSync();
 }