Fix typo in json.dart

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 239 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(Sink<String> sink) {
     if (sink is! StringConversionSink) {
       sink = new StringConversionSink.from(sink);
     } else if (sink is _Utf8EncoderSink) {
       return new _JsonUtf8EncoderSink(sink._sink, _toEncodable,
                                       JsonUtf8Encoder._utf8Encode(indent),
-                                      _JsonUtf8EncoderSink.DEFAULT_BUFFER_SIZE);
+                                      JsonUtf8Encoder.DEFAULT_BUFFER_SIZE);
     }
     return new _JsonEncoderSink(sink, _toEncodable, indent);
   }
 
   // Override the base-classes bind, to provide a better type.
   Stream<String> bind(Stream<Object> stream) => super.bind(stream);
 
   Converter<Object, dynamic> fuse(Converter<String, dynamic> other) {
     if (other is Utf8Encoder) {
       return new JsonUtf8Encoder(indent, _toEncodable);
@@ skipping 758 matching lines @@
         buffer.setRange(index, end, indent);
         index = end;
       } else {
         for (int i = 0; i < indentLength; i++) {
           writeByte(indent[i]);
         }
       }
     }
   }
 }