Modify tests to use Directory.systemTemp

tests/standalone/io/process_working_directory_test.dart

 // Copyright (c) 2012, 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.
 //
 // Process working directory test.
 
 library ProcessWorkingDirectoryTest;
 import "package:expect/expect.dart";
 import "dart:io";
 import "process_test_util.dart";
 
 class ProcessWorkingDirectoryTest {
   static String get fullTestFilePath {
     // Extract full path, since we run processes from another directory.
     File path = new File(getProcessTestFileName());
     Expect.isTrue(path.existsSync());
     return path.fullPathSync();
   }
 
   static void testValidDirectory() {
-    Directory directory = new Directory("").createTempSync();
+    Directory directory =
+        Directory.systemTemp.createTempSync('dart_process_working_directory');
     Expect.isTrue(directory.existsSync());
 
     Process.start(fullTestFilePath,
                   const ["0", "0", "99", "0"],
                   workingDirectory: directory.path)
         .then((process) {
           process.exitCode.then((int exitCode) {
             Expect.equals(exitCode, 99);
             directory.deleteSync();
           });
           process.stdout.listen((_) {});
           process.stderr.listen((_) {});
         }).catchError((error) {
           directory.deleteSync();
           Expect.fail("Couldn't start process");
         });
   }
 
   static void testInvalidDirectory() {
-    Directory directory = new Directory("").createTempSync();
+    Directory directory =
+        Directory.systemTemp.createTempSync('dart_process_working_directory');
     Expect.isTrue(directory.existsSync());
 
     Process.start(fullTestFilePath,
                   const ["0", "0", "99", "0"],
                   workingDirectory: directory.path + "/subPath")
         .then((process) {
           Expect.fail("bad process completed");
           directory.deleteSync();
         }).catchError((e) {
           Expect.isNotNull(e);
           directory.deleteSync();
         });
   }
 }
 
 
 
 main() {
   ProcessWorkingDirectoryTest.testValidDirectory();
   ProcessWorkingDirectoryTest.testInvalidDirectory();
 }