Reorganize barback's source files.

pkg/barback/test/stream_pool_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_pool_test;
 
 import 'dart:async';
 
-import 'package:barback/src/stream_pool.dart';
 import 'package:barback/src/utils.dart';
+import 'package:barback/src/utils/stream_pool.dart';
 import 'package:scheduled_test/scheduled_test.dart';
 
 import 'utils.dart';
 
 main() {
   initConfig();
 
   group("buffered", () {
     test("buffers events from multiple inputs", () {
       var pool = new StreamPool<String>();
@@ skipping 189 matching lines @@
           return pumpEventQueue();
         }).then((_) {
           pool.remove(broadcastController.stream);
           broadcastController.add("fourth");
           pool.close();
         }), completes);
       });
     });
   }
 }