Clean up dart:io exceptions.

sdk/lib/io/websocket.dart

 // Copyright (c) 2013, 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.
 
 part of dart.io;
 
 /**
  * Web socket status codes used when closing a web socket connection.
  */
 abstract class WebSocketStatus {
@@ skipping 135 matching lines @@
 
   /**
    * Sends data from a stream on web socket connection. Each data event from
    * [stream] will be send as a single WebSocket frame. The data from [stream]
    * must be either [:String:]s, or [:List<int>:]s holding bytes.
    */
   Future addStream(Stream stream);
 }
 
 
-class WebSocketException implements Exception {
+class WebSocketException implements IOException {
   const WebSocketException([String this.message = ""]);
   String toString() => "WebSocketException: $message";
   final String message;
 }