Run test tearDowns and clean up temporary directories when a signal is caught.

test/runner/browser/runner_test.dart

 // Copyright (c) 2015, 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.
 
 @TestOn("vm")
 
 import 'dart:io';
 
 import 'package:path/path.dart' as p;
 import 'package:test/src/util/exit_codes.dart' as exit_codes;
+import 'package:test/src/util/io.dart';
 import 'package:test/test.dart';
 
 import '../../io.dart';
 
 String _sandbox;
 
 final _success = """
 import 'dart:async';
 
 import 'package:test/test.dart';
 
 void main() {
   test("success", () {});
 }
 """;
 
 void main() {
   setUp(() {
-    _sandbox = Directory.systemTemp.createTempSync('test_').path;
+    _sandbox = createTempDir();
   });
 
   tearDown(() {
     new Directory(_sandbox).deleteSync(recursive: true);
   });
 
   group("fails gracefully if", () {
     test("a test file fails to compile", () {
       var testPath = p.join(_sandbox, "test.dart");
       new File(testPath).writeAsStringSync("invalid Dart file");
@@ skipping 133 matching lines @@
 """);
 
     var result = _runUnittest(["-p", "chrome", "test.dart"]);
     expect(result.stdout, contains("Hello,\nworld!\n"));
     expect(result.exitCode, equals(0));
   });
 }
 
 ProcessResult _runUnittest(List<String> args) =>
     runUnittest(args, workingDirectory: _sandbox);