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

sdk/lib/async/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.
 
 part of dart.async;
 
 // -------------------------------------------------------------------
 // Core Stream types
 // -------------------------------------------------------------------
 
@@ skipping 231 matching lines @@
 
   /**
    * Chains this stream as the input of the provided [StreamTransformer].
    *
    * Returns the result of [:streamTransformer.bind:] itself.
    */
   Stream transform(StreamTransformer<T, dynamic> streamTransformer) {
     return streamTransformer.bind(this);
   }
 
+  /**
+   * Reduces a sequence of values by repeatedly applying [combine].
+   *
+   * *WARNING UPCOMING API-CHANGE*: This method will be changed so that
+   * it doesn't take an initial value. Use [fold] instead.
+   */
+  Future reduce(var initialValue, combine(var previous, T element)) {
+    return fold(initialValue, combine);
+  }
+
   /** Reduces a sequence of values by repeatedly applying [combine]. */
-  Future reduce(var initialValue, combine(var previous, T element)) {
+  Future fold(var initialValue, combine(var previous, T element)) {
     _FutureImpl result = new _FutureImpl();
     var value = initialValue;
     StreamSubscription subscription;
     subscription = this.listen(
       // TODO(ahe): Restore type when feature is implemented in dart2js
       // checked mode. http://dartbug.com/7733
       (/*T*/ element) {
         _runUserCode(
           () => combine(value, element),
           (result) { value = result; },
@@ skipping 928 matching lines @@
 
 /* TODO(8997): Implement EventSink instead, */
 class _EventOutputSinkWrapper<T> extends StreamSink<T> {
   _EventOutputSink _sink;
   _EventOutputSinkWrapper(this._sink);
 
   void add(T data) { _sink._sendData(data); }
   void addError(AsyncError error) { _sink._sendError(error); }
   void close() { _sink._sendDone(); }
 }