added readAsString to pool

pkg/barback/lib/src/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.asset;
 
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
 
 import 'asset_id.dart';
+import 'file_pool.dart';
 import 'stream_replayer.dart';
 import 'utils.dart';
 
 /// A blob of content.
 ///
 /// Assets may come from the file system, or as the output of a [Transformer].
 /// They are identified by [AssetId].
 abstract class Asset {
   /// The ID for this asset.
   final AssetId id;
@@ skipping 70 matching lines @@
       }
     }
 
     buffer.write("]");
     return buffer.toString();
   }
 }
 
 /// An asset backed by a file on the local file system.
 class _FileAsset extends Asset {
+  /// Use a [FilePool] to handle reads so we can try to cope with running out
+  /// of file descriptors more gracefully.
+  static final _pool = new FilePool();
+
   final File _file;
   _FileAsset(AssetId id, this._file)
       : super(id);
 
   Future<String> readAsString({Encoding encoding}) {
     if (encoding == null) encoding = UTF8;
-    return _file.readAsString(encoding: encoding);
+    return _pool.readAsString(_file, encoding);
   }
 
-  Stream<List<int>> read() => _file.openRead();
+  Stream<List<int>> read() => _pool.openRead(_file);
 
   String toString() => 'File "${_file.path}"';
 }
 
 /// An asset whose data is stored in a string.
 class _StringAsset extends Asset {
   final String _contents;
 
   _StringAsset(AssetId id, this._contents)
       : super(id);
@@ skipping 38 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";
 }