Add a document-by-document JSON transformer.

lib/stream_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 'src/stream_channel_transformer.dart';
 
 export 'src/delegating_stream_channel.dart';
 export 'src/isolate_channel.dart';
+export 'src/json_document_transformer.dart';
 export 'src/multi_channel.dart';
 export 'src/stream_channel_completer.dart';
 export 'src/stream_channel_transformer.dart';
 
 /// An abstract class representing a two-way communication channel.
 ///
 /// Users should consider the [stream] emitting a "done" event to be the
 /// canonical indicator that the channel has closed. If they wish to close the
 /// channel, they should close the [sink]—canceling the stream subscription is
 /// not sufficient. Protocol errors may be emitted through the stream or through
@@ skipping 71 matching lines @@
 /// [stream] and [sink].
 abstract class StreamChannelMixin<T> implements StreamChannel<T> {
   void pipe(StreamChannel<T> other) {
     stream.pipe(other.sink);
     other.stream.pipe(sink);
   }
 
   StreamChannel transform(StreamChannelTransformer<dynamic, T> transformer) =>
       transformer.bind(this);
 }