Supporting non-SSVs in CustomEvent.detail

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/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
+class DartPayloadData {
+  final dartValue;
+
+  DartPayloadData(this.dartValue);
+}
+
 main() {
   useHtmlConfiguration();
 
   test('custom events', () {
     var provider = new EventStreamProvider<CustomEvent>('foo');
     var el = new DivElement();
 
     var fired = false;
     provider.forTarget(el).listen((ev) {
       fired = true;
@@ skipping 18 matching lines @@
       fired = true;
       expect(ev.detail, {'type': 'detail'});
     });
 
     var script = new ScriptElement();
     script.text = scriptContents;
     document.body.append(script);
 
     expect(fired, isTrue);
   });
+
+  test('custom events to JS', () {
+    var scriptContents = '''
+      window.addEventListener('dart_custom_event', function(e) {
+        if (e.detail == 'dart_message') {
+          e.preventDefault();
+        }
+      }, false);''';
+
+    document.body.append(new ScriptElement()..text = scriptContents);
+
+    var event = new CustomEvent('dart_custom_event', detail: 'dart_message');
+    window.dispatchEvent(event);
+    expect(event.defaultPrevented, isTrue);
+  });
+
+  test('custom data to Dart', () {
+    var data = new DartPayloadData(666);
+    var event = new CustomEvent('dart_custom_data_event', detail: data);
+
+    var future = window.on['dart_custom_data_event'].first.then((_) {
+      expect(event.detail.dartValue, 666);
+    });
+
+    document.body.dispatchEvent(event);
+    return future;
+  });
 }