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

client/html/generated/html/dartium/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 {
 
+  _DocumentEventsImpl get on() {
+    if (_on == null) _on = new _DocumentEventsImpl(_wrappedDocumentPtr);
+    return _on;
+  }
+
   Element get activeElement() => _wrap(_documentPtr.activeElement);
 
   Element get body() => _wrap(_documentPtr.body);
 
   void set body(Element value) { _documentPtr.body = _unwrap(value); }
 
   String get charset() => _wrap(_documentPtr.charset);
 
   void set charset(String value) { _documentPtr.charset = _unwrap(value); }
 
@@ skipping 28 matching lines @@
   Element get webkitCurrentFullScreenElement() => _wrap(_documentPtr.webkitCurrentFullScreenElement);
 
   bool get webkitFullScreenKeyboardInputAllowed() => _wrap(_documentPtr.webkitFullScreenKeyboardInputAllowed);
 
   bool get webkitHidden() => _wrap(_documentPtr.webkitHidden);
 
   bool get webkitIsFullScreen() => _wrap(_documentPtr.webkitIsFullScreen);
 
   String get webkitVisibilityState() => _wrap(_documentPtr.webkitVisibilityState);
 
-  _DocumentEventsImpl get on() {
-    if (_on == null) _on = new _DocumentEventsImpl(_wrappedDocumentPtr);
-    return _on;
-  }
-
   Range caretRangeFromPoint(int x, int y) {
     return _wrap(_documentPtr.caretRangeFromPoint(_unwrap(x), _unwrap(y)));
   }
 
   CDATASection createCDATASection(String data) {
     return _wrap(_documentPtr.createCDATASection(_unwrap(data)));
   }
 
   DocumentFragment createDocumentFragment() {
     return _wrap(_documentPtr.createDocumentFragment());
@@ skipping 195 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');
 }