convert method
- @override
 
override
    Converts input and returns the result of the conversion.
Implementation
@override
Digest convert(List<int> data) {
  var innerSink = new DigestSink();
  var outerSink = startChunkedConversion(innerSink);
  outerSink.add(data);
  outerSink.close();
  return innerSink.value;
}