Fix streams_test.

tests/html/streams_test.dart

 library streams_test;
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 import 'dart:async';
 import 'dart:html';
 
 class StreamHelper {
   var _a;
   StreamHelper() {
     _a = new TextInputElement();
@@ skipping 94 matching lines @@
     expect(callCount, 1);
 
     subscription.pause();
     helper.pulse();
     expect(callCount, 1);
 
     subscription.resume();
     helper.pulse();
     expect(callCount, 2);
 
-    var completer = new Completer<int>();
+    var completer = new Completer<int>.sync();
     subscription.pause(completer.future);
     helper.pulse();
     expect(callCount, 2);
 
     // Paused, should have no impact.
     subscription.pause();
     helper.pulse();
     subscription.resume();
     helper.pulse();
     expect(callCount, 2);
@@ skipping 141 matching lines @@
   });
 
   test('singleWhere', () {
     stream.singleWhere((_) => true).then((_) {});
   });
 
   test('elementAt', () {
     stream.elementAt(0).then((_) {});
   });
 }