Modernize the package's style.

lib/src/stream_sink_completer.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_completer;
-
 import 'dart:async';
 
 import 'null_stream_sink.dart';
 
 /// A [sink] where the destination is provided later.
 ///
 /// The [sink] is a normal sink that you can add events to to immediately, but
 /// until [setDestinationSink] is called, the events will be buffered.
 ///
 /// The same effect can be achieved by using a [StreamController] and adding it
@@ skipping 154 matching lines @@
           .catchError((_) {});
     }
 
     // If the user has already asked when the sink is done, connect the sink's
     // done callback to that completer.
     if (_doneCompleter != null) {
       _doneCompleter.complete(sink.done);
     }
   }
 }