Use the new web_socket_channel package.

lib/src/barback/web_socket_api.dart

 // Copyright (c) 2014, 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.
 
 import 'dart:async';
 import 'dart:io';
 
-import 'package:http_parser/http_parser.dart';
 import 'package:path/path.dart' as path;
 import 'package:json_rpc_2/json_rpc_2.dart' as json_rpc;
+import 'package:web_socket_channel/web_socket_channel.dart';
 
 import '../exit_codes.dart' as exit_codes;
 import '../io.dart';
 import '../log.dart' as log;
 import '../utils.dart';
 import 'asset_environment.dart';
 
 /// Implements the [WebSocket] API for communicating with a running pub serve
 /// process, mainly for use by the Editor.
 ///
@@ skipping 277 matching lines @@
 }
 
 /// The pub-specific JSON RPC error codes.
 class _Error {
   /// The specified directory is not being served.
   static const NOT_SERVED = 1;
 
   /// The specified directory overlaps one or more ones already being served.
   static const OVERLAPPING = 2;
 }