Converting tests over to using event streams.

tests/html/events_test.dart

 library EventsTest;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:html';
 
 main() {
   useHtmlConfiguration();
   test('TimeStamp', () {
     Event event = new Event('test');
 
@@ skipping 11 matching lines @@
     void handler(Event e) {
       expect(e.type, equals('test'));
       Element target = e.target;
       expect(element, equals(target));
       invocationCounter++;
     }
 
     Event event = new Event('test');
 
     invocationCounter = 0;
-    element.on['test'].dispatch(event);
+    element.dispatchEvent(event);
     expect(invocationCounter, isZero);
 
-    element.on['test'].add(handler, false);
+    var provider = new EventStreamProvider<CustomEvent>('test');
+
+    var sub = provider.forTarget(element).listen(handler);
     invocationCounter = 0;
-    element.on['test'].dispatch(event);
+    element.dispatchEvent(event);
     expect(invocationCounter, 1);
 
-    element.on['test'].remove(handler, false);
+    sub.cancel();
     invocationCounter = 0;
-    element.on['test'].dispatch(event);
+    element.dispatchEvent(event);
     expect(invocationCounter, isZero);
 
-    element.on['test'].add(handler, false);
+    provider.forTarget(element).listen(handler);
     invocationCounter = 0;
-    element.on['test'].dispatch(event);
+    element.dispatchEvent(event);
     expect(invocationCounter, 1);
 
-    element.on['test'].add(handler, false);
+    provider.forTarget(element).listen(handler);
     invocationCounter = 0;
-    element.on['test'].dispatch(event);
+    element.dispatchEvent(event);
     expect(invocationCounter, 1);
   });
   test('InitMouseEvent', () {
     DivElement div = new Element.tag('div');
     MouseEvent event = new MouseEvent('zebra', relatedTarget: div);
   });
 }