startChunkedConversion method
Starts a chunked conversion.
The returned sink serves as input for the long-running conversion. The
given sink serves as output.
Implementation
@override
dart_convert.StringConversionSink startChunkedConversion(
    Sink<List<int>> sink) {
  dart_convert.ByteConversionSink byteSink;
  if (sink is dart_convert.ByteConversionSink) {
    byteSink = sink;
  } else {
    byteSink = dart_convert.ByteConversionSink.from(sink);
  }
  return BaseEncoderSink(byteSink, this);
}