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

sdk/lib/_collection_dev/iterable.dart

 // Copyright (c) 2011, 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._collection.dev;
 
 /**
  * An [Iterable] for classes that have efficient [length] and [elementAt].
  *
  * All other methods are implemented in terms of [length] and [elementAt],
@@ skipping 182 matching lines @@
       }
       return buffer.toString();
     }
   }
 
   Iterable<E> where(bool test(E element)) => super.where(test);
 
   Iterable map(f(E element)) => new MappedListIterable(this, f);
 
   reduce(var initialValue, combine(var previousValue, E element)) {
+    return fold(initialValue, combine);
+  }
+
+  fold(var initialValue, combine(var previousValue, E element)) {
     var value = initialValue;
     int length = this.length;
     for (int i = 0; i < length; i++) {
       value = combine(value, elementAt(i));
       if (length != this.length) {
         throw new ConcurrentModificationError(this);
       }
     }
     return value;
   }
@@ skipping 450 matching lines @@
 
   E max([int compare(E a, E b)]) => null;
 
   String join([String separator]) => "";
 
   Iterable<E> where(bool test(E element)) => this;
 
   Iterable map(f(E element)) => const EmptyIterable();
 
   reduce(var initialValue, combine(var previousValue, E element)) {
+    return fold(initialValue, combine);
+  }
+
+  fold(var initialValue, combine(var previousValue, E element)) {
     return initialValue;
   }
 
   Iterable<E> skip(int count) => this;
 
   Iterable<E> skipWhile(bool test(E element)) => this;
 
   Iterable<E> take(int count) => this;
 
   Iterable<E> takeWhile(bool test(E element)) => this;
 
   List toList({ bool growable: true }) => growable ? <E>[] : new List<E>(0);
 
   Set toSet() => new Set<E>();
 }
 
 /** The always empty iterator. */
 class EmptyIterator<E> implements Iterator<E> {
   const EmptyIterator();
   bool moveNext() => false;
   E get current => null;
 }
 
 /** An [Iterator] that can move in both directions. */
 abstract class BidirectionalIterator<T> implements Iterator<T> {
   bool movePrevious();
 }