Make JSON parsing work as a chunked conversion sink.

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;
 
 /**
  * Error thrown by JSON serialization if an object cannot be serialized.
  *
  * The [unsupportedObject] field holds that object that failed to be serialized.
@@ skipping 308 matching lines @@
    * Throws [FormatException] if the input is not valid JSON text.
    */
   dynamic convert(String input) => _parseJson(input, _reviver);
 
   /**
    * Starts a conversion from a chunked JSON string to its corresponding
    * 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));
 
 
 // Implementation of encoder/stringifier.
 
 Object _defaultToEncodable(object) => object.toJson();
 
 class _JsonStringifier {
   // Character code constants.
@@ skipping 253 matching lines @@
         _sink.writeln();
         _indentLevel--;
         _write('}');
       }
       _seen.remove(object);
       return true;
     }
     return super.stringifyJsonValue(object);
   }
 }