Cleaning up event constructors

tools/dom/templates/html/impl/impl_Event.darttemplate

 // 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.
 
 // WARNING: Do not edit - generated code.
 
 part of html;
 
 $(ANNOTATIONS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   // 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 $CLASSNAME(String type,
-      [bool canBubble = true, bool cancelable = true]) {
-    return new Event.eventType('Event', type, canBubble, cancelable);
+      {bool canBubble: true, bool cancelable: true}) {
+    return new Event.eventType('Event', type, canBubble: canBubble,
+        cancelable: canBubble);
   }
 
   /**
    * 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);
    */
-  factory Event.eventType(String type, String name, [bool canBubble = true,
-      bool cancelable = true]) {
+  factory Event.eventType(String type, String name, {bool canBubble: true,
+      bool cancelable: true}) {
     final Event e = document.$dom_createEvent(type);
     e.$dom_initEvent(name, canBubble, cancelable);
     return e;
   }
 $!MEMBERS
 
   /**
    * Checks to see if the event class is supported by the current platform.
    */
   static bool _isTypeSupported(String eventType) {
     // Browsers throw for unsupported event names.
     try {
       var e = document.$dom_createEvent(eventType);
       return e is Event;
     } catch (_) { }
     return false;
   }
 }