Fix all strong-mode errors and warnings.

lib/src/channel.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:convert' as convert;
 
 import 'package:async/async.dart';
 import 'package:crypto/crypto.dart';
 import 'package:stream_channel/stream_channel.dart';
@@ skipping 86 matching lines @@
 }
 
 /// The sink exposed by a [WebSocketChannel].
 ///
 /// This is like a normal [StreamSink], except that it supports extra arguments
 /// to [close].
 class WebSocketSink extends DelegatingStreamSink {
   final WebSocketImpl _webSocket;
 
   WebSocketSink._(WebSocketImpl webSocket)
-      : super(webSocket),
-        _webSocket = webSocket;
+      : _webSocket = webSocket,
+        super(webSocket);
 
   /// Closes the web socket connection.
   ///
   /// [closeCode] and [closeReason] are the [close code][] and [reason][] sent
   /// to the remote peer, respectively. If they are omitted, the peer will see
   /// a "no status received" code with no reason.
   ///
   /// [close code]: https://tools.ietf.org/html/rfc6455#section-7.1.5
   /// [reason]: https://tools.ietf.org/html/rfc6455#section-7.1.6
   Future close([int closeCode, String closeReason]) =>
       _webSocket.close(closeCode, closeReason);
 }