Make JSON parsing work as a chunked conversion sink.

sdk/lib/convert/json.dart

Index: sdk/lib/convert/json.dart
diff --git a/sdk/lib/convert/json.dart b/sdk/lib/convert/json.dart
index 910b8cc4bb16af3df58490b71604a07dcea0ad81..4b7817fc390f7e3ee9bd3b7a3c983c7b26f9887f 100644
--- a/sdk/lib/convert/json.dart
+++ b/sdk/lib/convert/json.dart
@@ -326,39 +326,12 @@ class JsonDecoder extends Converter<String, Object> {
    *
    * The output [sink] receives exactly one decoded element through `add`.
    */
-  StringConversionSink startChunkedConversion(Sink<Object> sink) {
-    return new _JsonDecoderSink(_reviver, sink);
-  }
+  external StringConversionSink startChunkedConversion(Sink<Object> 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 Sink<Object> _sink;
-
-  _JsonDecoderSink(this._reviver, this._sink)
-      : super(new StringBuffer());
-
-  void close() {
-    super.close();
-    StringBuffer buffer = _stringSink;
-    String accumulated = buffer.toString();
-    buffer.clear();
-    Object decoded = _parseJson(accumulated, _reviver);
-    _sink.add(decoded);
-    _sink.close();
-  }
-}
-
 // Internal optimized JSON parsing implementation.
 external _parseJson(String source, reviver(key, value));