Fixed old docs for WebSocket.

sdk/lib/html/dart2js/html_dart2js.dart

 /// The Dart HTML library.
 library dart.dom.html;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:_collection-dev' hide Symbol;
 import 'dart:html_common';
 import 'dart:indexed_db';
 import 'dart:isolate';
 import 'dart:json' as json;
@@ skipping 22502 matching lines @@
  * To send data on the WebSocket, use the [send] method.
  *
  *     if (webSocket != null && webSocket.readyState == WebSocket.OPEN) {
  *       webSocket.send(data);
  *     } else {
  *       print('WebSocket not connected, message $data not sent');
  *     }
  *
  * To receive data on the WebSocket, register a listener for message events.
  *
- *     webSocket.on.message.add((MessageEvent e) {
+ *     webSocket.onMessage.listen((MessageEvent e) {
  *       receivedData(e.data);
  *     });
  *
  * The message event handler receives a [MessageEvent] object
  * as its sole argument.
  * You can also define open, close, and error handlers,
  * as specified by [WebSocketEvents].
  *
  * For more information, see the
  * [WebSockets](http://www.dartlang.org/docs/library-tour/#html-websockets)
@@ skipping 7071 matching lines @@
       _position = nextPosition;
       return true;
     }
     _current = null;
     _position = _array.length;
     return false;
   }
 
   T get current => _current;
 }