Fixed old docs for WebSocket.

tools/dom/docs/docs.json

 {
   "dart.dom.html": {
     "CanvasGradient": {
       "comment": [
         "/**",
         " * An opaque canvas object representing a gradient.",
         " *",
         " * Created by calling [createLinearGradient] or [createRadialGradient] on a",
         " * [CanvasRenderingContext2D] object.",
         " *",
@@ skipping 345 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 238 matching lines @@
           "   *",
           "   * [oldVersion] should match the database's current [version] exactly.",
           "   *",
           "   * * [Database.changeVersion](http://www.w3.org/TR/webdatabase/#dom-database-changeversion) from W3C.",
           "   */"
         ]
       }
     }
   }
 }