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

tools/dom/src/dartium_KeyEvent.dart

Index: tools/dom/src/dartium_KeyEvent.dart
diff --git a/tools/dom/src/dartium_KeyEvent.dart b/tools/dom/src/dartium_KeyEvent.dart
index 6be8d67ffbd36850fdff0fca274c0d821f43d26d..f225a9dc611b73844078ba3b02ea55b24413ae40 100644
--- a/tools/dom/src/dartium_KeyEvent.dart
+++ b/tools/dom/src/dartium_KeyEvent.dart
@@ -12,6 +12,7 @@
  */
 part of html;
 
+@Experimental()
 class KeyEvent extends _WrappedEvent implements KeyboardEvent {
   /** The parent KeyboardEvent that this KeyEvent is wrapping and "fixing". */
   KeyboardEvent _parent;
@@ -47,13 +48,28 @@ class KeyEvent extends _WrappedEvent implements KeyboardEvent {
   bool get _realAltKey => _parent.altKey;
 
   /** Construct a KeyEvent with [parent] as the event we're emulating. */
-  KeyEvent(KeyboardEvent parent): super(parent) {
+  KeyEvent.wrap(KeyboardEvent parent): super(parent) {
     _parent = parent;
     _shadowAltKey = _realAltKey;
     _shadowCharCode = _realCharCode;
     _shadowKeyCode = _realKeyCode;
   }
 
+  /** Programmatically create a new KeyEvent (and KeyboardEvent). */
+   KeyEvent(String type,
+      {Window view, bool canBubble: true, bool cancelable: true, int keyCode: 0,
+      int charCode: 0, int keyLocation: 1, bool ctrlKey: false,
+      bool altKey: false, bool shiftKey: false, bool metaKey: false,
+      bool altGraphKey: false}) {
+     _parent = new KeyboardEvent(type, view: view, canBubble: canBubble,
+        cancelable: cancelable, keyLocation: keyLocation, ctrlKey: ctrlKey,
+        altKey: altKey, shiftKey: shiftKey, metaKey: metaKey, altGraphKey:
+        altGraphKey);
+      _shadowAltKey = altKey;
+      _shadowCharCode = charCode;
+      _shadowKeyCode = keyCode;
+   }
+
   /** Accessor to provide a stream of KeyEvents on the desired target. */
   static EventStreamProvider<KeyEvent> keyDownEvent =
     new _KeyboardEventHandler('keydown');