Modernize the package's style.

lib/src/stream_sink_transformer/handler_transformer.dart

 // Copyright (c) 2016, 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.
 
-library async.stream_sink_transformer.handler_transformer;
-
 import 'dart:async';
 
 import '../stream_sink_transformer.dart';
 import '../delegate/stream_sink.dart';
 
 /// The type of the callback for handling data events.
 typedef void HandleData<S, T>(S data, EventSink<T> sink);
 
 /// The type of the callback for handling error events.
 typedef void HandleError<T>(
@@ skipping 81 matching lines @@
 class _SafeCloseSink<T> extends DelegatingStreamSink<T> {
   _SafeCloseSink(StreamSink<T> inner) : super(inner);
 
   Future close() => super.close().catchError((_) {});
 }
 
 /// A function to pass as a [StreamTransformer]'s `handleDone` callback.
 void _closeSink(EventSink sink) {
   sink.close();
 }