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

test/runner/browser/compiler_pool_test.dart

Index: test/runner/browser/compiler_pool_test.dart
diff --git a/test/runner/browser/compiler_pool_test.dart b/test/runner/browser/compiler_pool_test.dart
index ed28f052e133d35d36bcf3f56d21ab6fd15ddafe..6b05a3a15d22e01639d0acd39c171533fdf90b8b 100644
--- a/test/runner/browser/compiler_pool_test.dart
+++ b/test/runner/browser/compiler_pool_test.dart
@@ -8,6 +8,7 @@ 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';
@@ -16,7 +17,7 @@ String _sandbox;
 
 void main() {
   setUp(() {
-    _sandbox = Directory.systemTemp.createTempSync('test_').path;
+    _sandbox = createTempDir();
   });
 
   tearDown(() {