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

runtime/bin/vmstats/bargraph.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.vmstats;
 
 class BarGraph {
   CanvasElement _canvas;
   GraphModel _model;
   List<Element> _elements;
@@ skipping 200 matching lines @@
   List<int> _segments;
 
   Sample(this._segments) {}
 
   int get length => _segments.length;
   int operator[](int i) => _segments[i];
 
   Iterator<int> get iterator => _segments.iterator;
 
   int total() {
-    return _segments.reduce(0, (int prev, int element) => prev + element);
+    return _segments.fold(0, (int prev, int element) => prev + element);
   }
 }