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

tools/dom/src/EventStreamProvider.dart

Index: tools/dom/src/EventStreamProvider.dart
diff --git a/tools/dom/src/EventStreamProvider.dart b/tools/dom/src/EventStreamProvider.dart
index a9c293da5da7083b938ffbd80785bdea4cf32068..dc23c4fe8975efad8979026d02bcb1a92ec6f20a 100644
--- a/tools/dom/src/EventStreamProvider.dart
+++ b/tools/dom/src/EventStreamProvider.dart
@@ -90,6 +90,49 @@ class _ElementListEventStreamImpl<T extends Event> extends Stream<T>
 }
 
 /**
+ * A stream of custom events, which enables the user to "fire" (add) their own
+ * custom events to a stream.
+ */
+abstract class CustomStream<T extends Event> implements Stream<T> {
+  /**
+   * Add the following custom event to the stream for dispatching to interested
+   * listeners.
+   */
+  void add(T event);

[strom, 2013/09/12 15:42:41]

I understand using add() here, especially since it has the same signature as the
EventSink version. Still, I would imagine that it would be confusing to some
since you need a stream controller/sink everywhere else.

Maybe dispatch?

KeyEvent.
  keyPressEvent.
  forTarget(document.body).
  dispatch(new KeyEvent(...));

+}
+
+class _CustomEventStreamImpl<T extends Event> extends Stream<T>
+    implements CustomStream<T> {
+  StreamController<T> _streamController;
+  /** The type of event this stream is providing (e.g. "keydown"). */
+  String _type;
+
+  _CustomEventStreamImpl(String type) {
+    _type = type;
+    _streamController = new StreamController.broadcast(sync: true);
+  }
+
+  // Delegate all regular Stream behavior to our wrapped Stream.
+  StreamSubscription<T> listen(void onData(T event),
+      { void onError(error),
+        void onDone(),
+        bool cancelOnError}) {
+    return _streamController.stream.listen(onData, onError: onError,
+        onDone: onDone, cancelOnError: cancelOnError);
+  }
+
+  Stream<T> asBroadcastStream({void onListen(StreamSubscription subscription),
+                               void onCancel(StreamSubscription subscription)})
+      => _streamController.stream;
+
+  bool get isBroadcast => true;
+
+  void add(T event) {
+    if (event.type == _type) _streamController.add(event);
+  }
+}
+
+/**
  * A pool of streams whose events are unified and emitted through a central
  * stream.
  */