Add dummy dart:html library for documentation.

lib/html/doc/interface/WebSocket.dartdoc

+// 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.
+
+// WARNING:
+//   This file contains documentation that is merged into the real source.
+//   Do not make code changes here.
+
+/// @domName WebSocket
+interface WebSocket extends EventTarget default _WebSocketFactoryProvider {
+
+  WebSocket(String url);
+
+  /**
+   * @domName EventTarget.addEventListener, EventTarget.removeEventListener, EventTarget.dispatchEvent
+   */
+  WebSocketEvents get on();
+
+  static final int CLOSED = 3;
+
+  static final int CLOSING = 2;
+
+  static final int CONNECTING = 0;
+
+  static final int OPEN = 1;
+
+  /** @domName WebSocket.URL */
+  final String URL;
+
+  /** @domName WebSocket.binaryType */
+  String binaryType;
+
+  /** @domName WebSocket.bufferedAmount */
+  final int bufferedAmount;
+
+  /** @domName WebSocket.extensions */
+  final String extensions;
+
+  /** @domName WebSocket.protocol */
+  final String protocol;
+
+  /** @domName WebSocket.readyState */
+  final int readyState;
+
+  /** @domName WebSocket.url */
+  final String url;
+
+  /** @domName WebSocket.addEventListener */
+  void $dom_addEventListener(String type, EventListener listener, [bool useCapture]);
+
+  /** @domName WebSocket.close */
+  void close([int code, String reason]);
+
+  /** @domName WebSocket.dispatchEvent */
+  bool $dom_dispatchEvent(Event evt);
+
+  /** @domName WebSocket.removeEventListener */
+  void $dom_removeEventListener(String type, EventListener listener, [bool useCapture]);
+
+  /** @domName WebSocket.send */
+  bool send(String data);
+}
+
+interface WebSocketEvents extends Events {
+
+  EventListenerList get close();
+
+  EventListenerList get error();
+
+  EventListenerList get message();
+
+  EventListenerList get open();
+}