Converting tests over to using event streams.

tests/html/js_interop_1_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 JsInterop1Test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 injectSource(code) {
   final script = new ScriptElement();
   script.type = 'text/javascript';
   script.innerHtml = code;
   document.body.nodes.add(script);
 }
 
 main() {
   useHtmlConfiguration();
   var callback;
 
   test('js-to-dart-post-message', () {
-    var onSuccess = expectAsync1((e) {
-      window.on.message.remove(callback);
-    });
-    callback = (e) {
-      if (e.data == 'hello') {
-        onSuccess(e);
-      }
-    };
-    window.on.message.add(callback);
+    var subscription = null;
+    var complete = false;
+    subscription = window.onMessage.listen(expectAsyncUntil1(
+        (e) {
+          if (e.data == 'hello') {
+            subscription.cancel();
+            complete = true;
+          }
+        },
+        () => complete));
     injectSource("window.postMessage('hello', '*');");
   });
 }