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

tools/dom/templates/html/dart2js/html_dart2js.darttemplate

Index: tools/dom/templates/html/dart2js/html_dart2js.darttemplate
diff --git a/tools/dom/templates/html/dart2js/html_dart2js.darttemplate b/tools/dom/templates/html/dart2js/html_dart2js.darttemplate
index 23b7818544e62d9ee43e127edb94721e56b2b617..80622e130c4d9a2ccb77bd8df82632c3ce0b6c9b 100644
--- a/tools/dom/templates/html/dart2js/html_dart2js.darttemplate
+++ b/tools/dom/templates/html/dart2js/html_dart2js.darttemplate
@@ -49,10 +49,11 @@ 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;