Default to UTF-8 in the HTTP package.

pkg/http/lib/src/byte_stream.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 byte_stream;
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:typed_data';
 
@@ skipping 17 matching lines @@
       return buffer;
     }).then(toUint8List);
   }
 
   /// Collect the data of this stream in a [String], decoded according to
   /// [encoding], which defaults to `Encoding.UTF_8`.
   Future<String> bytesToString([Encoding encoding=Encoding.UTF_8]) =>
       toBytes().then((bytes) => decodeString(bytes, encoding));
 
   Stream<String> toStringStream([Encoding encoding=Encoding.UTF_8]) =>
-      map((bytes) => decodeString(bytes, encoding));
+    transform(new StringDecoder(encoding));
 }