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

tools/dom/templates/html/dart2js/html_dart2js.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.
 
 // DO NOT EDIT - unless you are editing documentation as per:
 // https://code.google.com/p/dart/wiki/ContributingHTMLDocumentation
 // Auto-generated dart:html library.
 
 /**
  * HTML elements and other resources for web-based applications that need to
@@ skipping 31 matching lines @@
 import 'dart:math';
 import 'dart:typed_data';
 // Not actually used, but imported since dart:html can generate these objects.
 import 'dart:svg' as svg;
 import 'dart:web_audio' as web_audio;
 import 'dart:web_gl' as gl;
 import 'dart:web_sql';
 import 'dart:_js_helper' show
     convertDartClosureToJS, Creates, JavaScriptIndexingBehavior,
     JSName, Null, Returns,
-    findDispatchTagForInterceptorClass, setNativeSubclassDispatchRecord;
+    findDispatchTagForInterceptorClass, setNativeSubclassDispatchRecord,
+    makeLeafDispatchRecord;
 import 'dart:_interceptors' show
     Interceptor, JSExtendableArray, findInterceptorConstructorForType,
-    getNativeInterceptor;
+    getNativeInterceptor, setDispatchProperty;
 import 'dart:_isolate_helper' show IsolateNatives;
 import 'dart:_foreign_helper' show JS;
 
 export 'dart:math' show Rectangle, Point;
 
 $!GENERATED_DART_FILES
 
 part '$AUXILIARY_DIR/AttributeMap.dart';
 part '$AUXILIARY_DIR/CanvasImageSource.dart';
 part '$AUXILIARY_DIR/CrossFrameTypes.dart';
@@ skipping 72 matching lines @@
   if (JS('bool', r'!window.$dart$isolate$counter')) {
     JS('void', r'window.$dart$isolate$counter = 1');
   }
   return JS('int', r'window.$dart$isolate$counter++');
 }
 
 // Fast path to invoke JS send port.
 _callPortSync(int id, message) {
   return JS('var', r'ReceivePortSync.dispatchCall(#, #)', id, message);
 }