Fully polyfill KeyEvent so that you can programmatically create your own "keyboard" events.

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 $LIBRARYNAME;
 
 $(ANNOTATIONS)$(CLASS_MODIFIERS)class $CLASSNAME$EXTENDS$IMPLEMENTS$NATIVESPEC {
   // In JS, canBubble and cancelable are technically required parameters to
@@ skipping 15 matching lines @@
    * 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}) {
     final Event e = document._createEvent(type);
     e._initEvent(name, canBubble, cancelable);
     return e;
   }
+
+  $CLASSNAME._private();
 $!MEMBERS
 }