Converting tests over to using event streams.

tests/html/history_test.dart

 library HistoryTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_individual_config.dart';
 import 'dart:html';
 
-/// Waits for a callback once, then removes the event handler.
-void expectAsync1Once(EventListenerList list, void callback(arg)) {
-  var fn = null;
-  fn = expectAsync1((arg) {
-    list.remove(fn);
-    callback(arg);
-  });
-  list.add(fn);
-}
-
 main() {
   useHtmlIndividualConfiguration();
 
   group('supported_state', () {
     test('supportsState', () {
       expect(History.supportsState, true);
     });
   });
 
   group('supported_HashChangeEvent', () {
@@ skipping 20 matching lines @@
     test('back', () {
       expect(() {
         window.history.pushState(null, document.title, '?dummy1');
         window.history.pushState(null, document.title, '?dummy2');
         var length = window.history.length;
 
         expect(window.location.href.endsWith('dummy2'), isTrue);
 
         // Need to wait a frame or two to let the pushState events occur.
         window.setTimeout(expectAsync0(() {
-          expectAsync1Once(window.on.popState, (_) {
+          window.onPopState.first.then(expectAsync1((_){
             expect(window.history.length, length);
             expect(window.location.href.endsWith('dummy1'), isTrue);
-          });
+          }));
 
           window.history.back();
         }), 100);
       }, expectation);
     });
 
     test('replaceState', () {
       expect(() {
         var length = window.history.length;
 
@@ skipping 14 matching lines @@
       var expectation = HashChangeEvent.supported ? returnsNormally : throws;
       expect(() {
         var event = new HashChangeEvent('change', oldUrl:'old', newUrl: 'new');
         expect(event is HashChangeEvent, true);
         expect(event.oldUrl, 'old');
         expect(event.newUrl, 'new');
       }, expectation);
     });
   });
 }