Re-write _BufferList to keep an internal Uint8List buffer, that will grow on demand.

sdk/lib/io/file_impl.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.
 
 part of dart.io;
 
 // Read the file in blocks of size 64k.
 const int _BLOCK_SIZE = 64 * 1024;
 
 
@@ skipping 460 matching lines @@
     return new IOSink(consumer, encoding: encoding);
   }
 
   Future<List<int>> readAsBytes() {
     _ensureFileService();
     Completer<List<int>> completer = new Completer<List<int>>();
     var chunks = new _BufferList();
     openRead().listen(
       (d) => chunks.add(d),
       onDone: () {
-        var result = chunks.readBytes(chunks.length);
-        if (result == null) result = <int>[];
+        var result = chunks.readBytes();
         completer.complete(result);
       },
       onError: (e) {
         completer.completeError(e);
       },
       cancelOnError: true);
     return completer.future;
   }
 
   List<int> readAsBytesSync() {
@@ skipping 545 matching lines @@
           new FileIOException("File closed '$_path'"));
     });
     return completer.future;
   }
 
   final String _path;
   int _id;
 
   SendPort _fileService;
 }