Add Iterable.fold (and Stream.fold) which replace `reduce`.

pkg/scheduled_test/test/descriptor/utils.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 test.descriptor.utils;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:scheduled_test/descriptor.dart' as d;
@@ skipping 14 matching lines @@
   currentSchedule.onComplete.schedule(() {
     d.defaultRoot = null;
     if (sandbox == null) return;
     var oldSandbox = sandbox;
     sandbox = null;
     return new Directory(oldSandbox).delete(recursive: true);
   });
 }
 
 Future<List<int>> byteStreamToList(Stream<List<int>> stream) {
-  return stream.reduce(<int>[], (buffer, chunk) {
+  return stream.fold(<int>[], (buffer, chunk) {
     buffer.addAll(chunk);
     return buffer;
   });
 }
 
 Future<String> byteStreamToString(Stream<List<int>> stream) =>
   byteStreamToList(stream).then((bytes) => new String.fromCharCodes(bytes));