Refactor the event-generation code to locate it in systemhtml.py.

client/html/generated/html/frog/Document.dart

 // Copyright (c) 2012, 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 _DocumentImpl extends _ElementImpl
     implements Document
     native "*HTMLHtmlElement" {
 
+  _DocumentEventsImpl get on() =>
+    new _DocumentEventsImpl(_jsDocument);
+
   _ElementImpl get activeElement() native "return this.parentNode.activeElement;";
 
   _ElementImpl get body() native "return this.parentNode.body;";
 
   void set body(_ElementImpl value) native "this.parentNode.body = value;";
 
   String get charset() native "return this.parentNode.charset;";
 
   void set charset(String value) native "this.parentNode.charset = value;";
 
@@ skipping 28 matching lines @@
   _ElementImpl get webkitCurrentFullScreenElement() native "return this.parentNode.webkitCurrentFullScreenElement;";
 
   bool get webkitFullScreenKeyboardInputAllowed() native "return this.parentNode.webkitFullScreenKeyboardInputAllowed;";
 
   bool get webkitHidden() native "return this.parentNode.webkitHidden;";
 
   bool get webkitIsFullScreen() native "return this.parentNode.webkitIsFullScreen;";
 
   String get webkitVisibilityState() native "return this.parentNode.webkitVisibilityState;";
 
-  _DocumentEventsImpl get on() =>
-    new _DocumentEventsImpl(_jsDocument);
-
   _RangeImpl caretRangeFromPoint(int x, int y) native "return this.parentNode.caretRangeFromPoint(x, y);";
 
   _CDATASectionImpl createCDATASection(String data) native "return this.parentNode.createCDATASection(data);";
 
   _DocumentFragmentImpl createDocumentFragment() native "return this.parentNode.createDocumentFragment();";
 
   _ElementImpl _createElement(String tagName) native "return this.parentNode.createElement(tagName);";
 
   _EventImpl _createEvent(String eventType) native "return this.parentNode.createEvent(eventType);";
 
@@ skipping 142 matching lines @@
   EventListenerList get submit() => _get('submit');
 
   EventListenerList get touchCancel() => _get('touchcancel');
 
   EventListenerList get touchEnd() => _get('touchend');
 
   EventListenerList get touchMove() => _get('touchmove');
 
   EventListenerList get touchStart() => _get('touchstart');
 }