Modified unittest to use new argument syntax.

tests/html/event_customevent_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.
 
 #library('EventCustomEventTest');
 #import('../../pkg/unittest/unittest.dart');
 #import('../../pkg/unittest/html_config.dart');
 #import('dart:html');
 
 // TODO(nweiz): Make this private to testEvents when Frog supports closures with
 // optional arguments.
 eventTest(String name, Event eventFn(), void validate(Event),
     [String type = 'foo']) {
   test(name, () {
     final el = new Element.tag('div');
     var fired = false;
     el.on[type].add((ev) {
       fired = true;
       validate(ev);
     });
     el.on[type].dispatch(eventFn());
-    expect(fired, isTrue, 'Expected event to be dispatched.');
+    expect(fired, isTrue, reason: 'Expected event to be dispatched.');
   });
 }
 
 main() {
   useHtmlConfiguration();
 
   eventTest('CustomEvent.initCustomEvent', () {
     return new CustomEvent('foo', false, false, 'detail');
   },
   (ev) { expect(ev.detail, equals('detail')); });
 }