Remove default value in factory constructor.

tests/lib/async/event_helper.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 event_helper;
 
 import 'dart:async';
 
 abstract class Event {
   void replay(EventSink sink);
@@ skipping 55 matching lines @@
 
   Events();
 
   Events.fromIterable(Iterable iterable) {
     for (var value in iterable) add(value);
     close();
   }
 
   /** Capture events from a stream into a new [Events] object. */
   factory Events.capture(Stream stream,
-                         { bool cancelOnError: false }) = CaptureEvents;
+                         { bool cancelOnError }) = CaptureEvents;
 
   // EventSink interface.
   void add(var value) {
     if (trace) print("Events#$hashCode: add($value)");
     events.add(new DataEvent(value));
   }
 
   void addError(error, [StackTrace stackTrace]) {
     if (trace) print("Events#$hashCode: addError($error)");
     events.add(new ErrorEvent(error));
@@ skipping 86 matching lines @@
   void resume() {
     if (trace) print("Events#$hashCode: resume");
     subscription.resume();
   }
 
   void onDone(void action()) {
     if (trace) print("Events#$hashCode: onDone");
     super.onDone(action);
   }
 }