Register Document events on Document, not HTMLDocument.

client/html/src/DocumentWrappingImplementation.dart

 // Copyright (c) 2011, 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.
 
 class DocumentEventsImplementation extends ElementEventsImplementation
       implements DocumentEvents {
 
   DocumentEventsImplementation._wrap(_ptr) : super._wrap(_ptr);
 
   EventListenerList get readyStateChange() => _get('readystatechange');
@@ skipping 126 matching lines @@
   }
 
   /** @domName HTMLHtmlElement.manifest */
   String get manifest() => _ptr.manifest;
 
   /** @domName HTMLHtmlElement.manifest */
   void set manifest(String value) { _ptr.manifest = value; }
 
   DocumentEvents get on() {
     if (_on === null) {
-      _on = new DocumentEventsImplementation._wrap(_ptr);
+      _on = new DocumentEventsImplementation._wrap(_documentPtr);
     }
     return _on;
   }
 }