Modify tests to use Directory.systemTemp

tests/standalone/io/file_stat_test.dart

Index: tests/standalone/io/file_stat_test.dart
diff --git a/tests/standalone/io/file_stat_test.dart b/tests/standalone/io/file_stat_test.dart
index afd1b67a0adaf9b0f4c7e5e45985847338ab44eb..bca40aab0d59673a65267bb62ef88c3174da0cf8 100644
--- a/tests/standalone/io/file_stat_test.dart
+++ b/tests/standalone/io/file_stat_test.dart
@@ -12,7 +12,7 @@ import "package:expect/expect.dart";
 import "package:path/path.dart";
 
 void testStat() {
-  Directory directory = new Directory("").createTempSync();
+  Directory directory = Directory.createSystemTempSync('dart_file_stat');
   File file = new File(join(directory.path, "file"));
   Expect.throws(file.statSync);
   Expect.throws(() => FileStat.statSync(file.path));
@@ -48,7 +48,7 @@ void testStat() {
 
 
 Future testStatAsync() {
-  return new Directory("").createTemp()
+  return Directory.createSystemTemp('dart_file_stat')
   .then((directory) {
     File file = new File(join(directory.path, "file"));
     return FileStat.stat(file.path)