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

client/html/generated/html/frog/WebSocket.dart

Index: client/html/generated/html/frog/WebSocket.dart
diff --git a/client/html/generated/html/frog/WebSocket.dart b/client/html/generated/html/frog/WebSocket.dart
index 740d5cb80550cae4664babfd052c104a10ec7a37..e82b06e262a322e260f4f80cff992596d2a78080 100644
--- a/client/html/generated/html/frog/WebSocket.dart
+++ b/client/html/generated/html/frog/WebSocket.dart
@@ -1,6 +1,9 @@
 
 class _WebSocketImpl extends _EventTargetImpl implements WebSocket native "*WebSocket" {
 
+  _WebSocketEventsImpl get on() =>
+    new _WebSocketEventsImpl(this);
+
   static final int CLOSED = 3;
 
   static final int CLOSING = 2;
@@ -23,9 +26,6 @@ class _WebSocketImpl extends _EventTargetImpl implements WebSocket native "*WebS
 
   final String url;
 
-  _WebSocketEventsImpl get on() =>
-    new _WebSocketEventsImpl(this);
-
   void _addEventListener(String type, EventListener listener, [bool useCapture = null]) native "this.addEventListener(type, listener, useCapture);";
 
   void close([int code = null, String reason = null]) native;