Add transformer support to Converters.

sdk/lib/convert/converter.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;
 
 /**
  * A [Converter] converts data from one representation into another.
  *
  * *Converters are still experimental and are subject to change without notice.*
  *
  */
-abstract class Converter<S, T> {
+abstract class Converter<S, T> implements StreamTransformer {
   /**
    * Converts [input] and returns the result of the conversion.
    */
   T convert(S input);
 
   /**
    * Fuses `this` with [other].
    *
    * Encoding with the resulting converter is equivalent to converting with
    * `this` before converting with `other`.
    */
   Converter<S, dynamic> fuse(Converter<T, dynamic> other) {
     return new _FusedConverter<S, T, dynamic>(this, other);
   }
 
   /**
    * Starts a chunked conversion.
    */
   ChunkedConversionSink startChunkedConversion(ChunkedConversionSink sink) {
     throw new UnsupportedError(
         "This converter does not support chunked conversions: $this");
   }
+
+  // Subclasses are encouraged to provide better types.
+  Stream bind(Stream source) {
+    return new _ConverterTransformStream(source, this);
+  }
 }
 
 /**
  * Fuses two converters.
  *
  * For a non-chunked conversion converts the input in sequence.
  */
 class _FusedConverter<S, M, T> extends Converter<S, T> {
   final Converter _first;
   final Converter _second;
 
   _FusedConverter(this._first, this._second);
 
   T convert(S input) => _second.convert(_first.convert(input));
 
   ChunkedConversionSink startChunkedConversion(ChunkedConversionSink sink) {
     return _first.startChunkedConversion(_second.startChunkedConversion(sink));
   }
 }