Modernize the package's style.

lib/src/stream_completer.dart

 // Copyright (c) 2015, 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_completer;
-
 import "dart:async";
 
 /// A single-subscription [stream] where the contents are provided later.
 ///
 /// It is generally recommended that you never create a `Future<Stream>`
 /// because you can just directly create a stream that doesn't do anything
 /// until it's ready to do so.
 /// This class can be used to create such a stream.
 ///
 /// The [stream] is a normal stream that you can listen to immediately,
@@ skipping 162 matching lines @@
     _sourceStream = _controller.stream;  // Mark stream as set.
     _controller.close();
   }
 
   // Creates the [_controller].
   void _createController() {
     assert(_controller == null);
     _controller = new StreamController<T>(sync: true);
   }
 }