Add transformer support to Converters.

sdk/lib/convert/json.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.convert;
 
 /**
  * An instance of the default implementation of the [JsonCodec].
  *
  * This instance provides a convenient access to the most common JSON
@@ skipping 100 matching lines @@
    * Returns a chunked-conversion sink that accepts at most one object. It is
    * an error to invoke `add` more than once on the returned sink.
    */
   ChunkedConversionSink<Object> startChunkedConversion(
       ChunkedConversionSink<String> sink) {
     if (sink is! StringConversionSink) {
       sink = new StringConversionSink.from(sink);
     }
     return new _JsonEncoderSink(sink);
   }
+
+  // Override the base-classes bind, to provide a better type.
+  Stream<String> bind(Stream<Object> stream) => super.bind(stream);
 }
 
 /**
  * Implements the chunked conversion from object to its JSON representation.
  *
  * The sink only accepts one value, but will produce output in a chunked way.
  */
 class _JsonEncoderSink extends ChunkedConversionSink<Object> {
   final StringConversionSink _sink;
   bool _isDone = false;
@@ skipping 52 matching lines @@
   /**
    * Starts a conversion from a chunked JSON string to its corresponding
    * object.
    *
    * The output [sink] receives exactly one decoded element through `add`.
    */
   StringConversionSink startChunkedConversion(
       ChunkedConversionSink<Object> sink) {
     return new _JsonDecoderSink(_reviver, sink);
   }
+
+  // Override the base-classes bind, to provide a better type.
+  Stream<Object> bind(Stream<String> stream) => super.bind(stream);
 }
 
 /**
  * Implements the chunked conversion from a JSON string to its corresponding
  * object.
  *
  * The sink only creates one object, but its input can be chunked.
  */
 // TODO(floitsch): don't accumulate everything before starting to decode.
 class _JsonDecoderSink extends _StringSinkConversionSink {
   final _Reviver _reviver;
   final ChunkedConversionSink<Object> _chunkedSink;
 
   _JsonDecoderSink(this._reviver, this._chunkedSink)
       : super(new StringBuffer());
 
   void close() {
     super.close();
     StringBuffer buffer = _stringSink;
     String accumulated = buffer.toString();
     buffer.clear();
     Object decoded = OLD_JSON_LIB.parse(accumulated, _reviver);
     _chunkedSink.add(decoded);
     _chunkedSink.close();
   }
 }