Tighten up a bunch of types in test.dart.

tools/testing/dart/drt_updater.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.
 
 // TODO(antonm): rename to something like test_runner_updater.
 
 library drt_updater;
 
 import "dart:async";
 import "dart:io";
 
 import "test_suite.dart";
 
+typedef void Action();
+
 class _DartiumUpdater {
   String name;
   String script;
   String option;
 
   bool isActive = false;
   bool updated = false;
-  List onUpdated;
+  List<Action> onUpdated;
 
   Future<ProcessResult> _updatingProcess;
 
   _DartiumUpdater(this.name, this.script, [this.option = null]);
 
   void update() {
     if (!isActive) {
       isActive = true;
       print('Updating $name.');
       onUpdated = [
@@ skipping 49 matching lines @@
     // Download the default Dartium from Google Storage.
     if (_dartiumUpdater == null) {
       _dartiumUpdater = new _DartiumUpdater(
           'Dartium Chrome', 'tools/get_archive.py', 'dartium');
     }
     return _dartiumUpdater;
   } else {
     return null;
   }
 }