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

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

Index: client/html/generated/html/frog/Document.dart
diff --git a/client/html/generated/html/frog/Document.dart b/client/html/generated/html/frog/Document.dart
index 65601251a421c242022f939255af9a2c6ed1bda2..76e0ee99c6fc0cd4cfd59f9452b2b35fbdbecd87 100644
--- a/client/html/generated/html/frog/Document.dart
+++ b/client/html/generated/html/frog/Document.dart
@@ -6,6 +6,9 @@ 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;";
@@ -54,9 +57,6 @@ class _DocumentImpl extends _ElementImpl
 
   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);";