fix a bug in the Event constructor

sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev';
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
@@ skipping 9528 matching lines @@
 class Event native "Event" {
   // In JS, canBubble and cancelable are technically required parameters to
   // init*Event. In practice, though, if they aren't provided they simply
   // default to false (since that's Boolean(undefined)).
   //
   // Contrary to JS, we default canBubble and cancelable to true, since that's
   // what people want most of the time anyway.
   factory Event(String type,
       {bool canBubble: true, bool cancelable: true}) {
     return new Event.eventType('Event', type, canBubble: canBubble,
-        cancelable: canBubble);
+        cancelable: cancelable);
   }
 
   /**
    * Creates a new Event object of the specified type.
    *
    * This is analogous to document.createEvent.
    * Normally events should be created via their constructors, if available.
    *
    *     var e = new Event.type('MouseEvent', 'mousedown', true, true);
    */
@@ skipping 20032 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }