Fix all strong-mode errors and warnings.

lib/io.dart

 // Copyright (c) 2016, 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:async/async.dart';
 import 'package:stream_channel/stream_channel.dart';
 
@@ skipping 67 matching lines @@
         stream = stream.handleError((error) =>
             throw new WebSocketChannelException.from(error));
 }
 
 /// A [WebSocketSink] that forwards [close] calls to a `dart:io` [WebSocket].
 class _IOWebSocketSink extends DelegatingStreamSink implements WebSocketSink {
   /// The underlying socket.
   final WebSocket _webSocket;
 
   _IOWebSocketSink(WebSocket webSocket)
-      : super(webSocket),
-        _webSocket = webSocket;
+      : _webSocket = webSocket,
+        super(webSocket);
 
   Future close([int closeCode, String closeReason]) =>
       _webSocket.close(closeCode, closeReason);
 }