Reorganize barback's source files.

pkg/barback/lib/src/asset/internal_asset.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.internal_asset;
+library barback.asset.internal_asset;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:typed_data';
 
+import '../serialize.dart';
+import '../utils.dart';
+import '../utils/file_pool.dart';
+import '../utils/stream_replayer.dart';
 import 'asset.dart';
 import 'asset_id.dart';
-import 'file_pool.dart';
-import 'serialize.dart';
-import 'stream_replayer.dart';
-import 'utils.dart';
 
 /// Serialize an asset to a form that's safe to send across isolates.
 Map serializeAsset(Asset asset) {
   var id = serializeId(asset.id);
   if (asset is BinaryAsset) {
     return {
       'type': 'binary',
       'id': id,
       'contents': asset._contents
     };
@@ skipping 151 matching lines @@
   Future<String> readAsString({Encoding encoding}) {
     if (encoding == null) encoding = UTF8;
     return _replayer.getReplay().toList()
         .then((chunks) => encoding.decode(flatten(chunks)));
   }
 
   Stream<List<int>> read() => _replayer.getReplay();
 
   String toString() => "Stream";
 }