Reorganize barback's source files.

pkg/barback/test/stream_replayer_test.dart

 // Copyright (c) 2013, 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 barback.test.stream_replayer_test;
 
 import 'dart:async';
 
-import 'package:barback/src/stream_replayer.dart';
 import 'package:barback/src/utils.dart';
+import 'package:barback/src/utils/stream_replayer.dart';
 import 'package:unittest/unittest.dart';
 
 import 'utils.dart';
 
 main() {
   initConfig();
 
   test("a replay that's retrieved before the stream is finished replays the "
       "stream", () {
     var controller = new StreamController<int>();
@@ skipping 71 matching lines @@
     var controller = new StreamController<int>(onListen: () {
       isOpened = true;
     });
     var replayer = new StreamReplayer<int>(controller.stream);
     replayer.getReplay();
     replayer.getReplay();
 
     expect(pumpEventQueue().then((_) => isOpened), completion(isFalse));
   });
 }