Remove the html warnings!

tools/dom/src/EventStreamProvider.dart

 // Copyright (c) 2013, 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.
 
 part of html;
 
 /**
  * A factory to expose DOM events as Streams.
  */
 class EventStreamProvider<T extends Event> {
@@ skipping 410 matching lines @@
   }
 
   ElementStream<T> _forElementList(ElementList e,
       {bool useCapture: false}) {
     return new _ElementListEventStreamImpl(e, _eventTypeGetter(e), useCapture);
   }
 
   String getEventType(EventTarget target) {
     return _eventTypeGetter(target);
   }
+
+  String get _eventType =>
+      throw new UnsupportedError('Access type through getEventType method.');
 }