Modify tests to use Directory.systemTemp

tests/standalone/io/file_stat_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.
 //
 // Dart test program for testing dart:io FileSystemEntity.Stat().
 
 import 'dart:async';
 import 'dart:io';
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 import "package:path/path.dart";
 
 void testStat() {
-  Directory directory = new Directory("").createTempSync();
+  Directory directory = Directory.systemTemp.createTempSync('dart_file_stat');
   File file = new File(join(directory.path, "file"));
   Expect.throws(file.statSync);
   Expect.throws(() => FileStat.statSync(file.path));
   file.writeAsStringSync("Dart IO library test of FileStat");
   new Timer(const Duration(seconds: 2), () {
     file.readAsStringSync();
     directory.listSync();
     FileStat fileStat = FileStat.statSync(file.path);
     FileStat fileStatDirect = file.statSync();
     Expect.equals(FileSystemEntityType.FILE, fileStat.type);
@@ skipping 15 matching lines @@
       Expect.isTrue(
           directoryStat.changed.compareTo(directoryStat.accessed) < 0);
     }
     Expect.equals(7 << 6, directoryStat.mode & (7 << 6));  // Includes +urwx.
     directory.deleteSync(recursive: true);
   });
 }
 
 
 Future testStatAsync() {
-  return new Directory("").createTemp()
+  return Directory.systemTemp.createTemp('dart_file_stat')
   .then((directory) {
     File file = new File(join(directory.path, "file"));
     return FileStat.stat(file.path)
     .then((_) => Expect.fail("FileStat.stat should throw an exception."))
     .catchError((e) => null)
     .then((_) => file.stat())
     .then((_) => Expect.fail("File.stat should throw an exception."))
     .catchError((e) => null)
     .then((_) => file.writeAsString("Dart IO library test of FileStat"))
     .then((_) => new Future.delayed(const Duration(seconds: 2)))
@@ skipping 55 matching lines @@
     });
   });
 }
 
 
 void main() {
   asyncStart();
   testStat();
   testStatAsync().then((_) => asyncEnd());
 }