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

tests/standalone/io/zlib_test.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.
 
 import 'dart:async';
 import 'dart:io';
 import 'dart:isolate';
 
 void testZLibDeflate() {
   test(int level, List<int> expected) {
     var port = new ReceivePort();
     var data = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
     var controller = new StreamController();
     controller.stream.transform(new ZLibDeflater(gzip: false, level: level))
-        .reduce([], (buffer, data) {
+        .fold([], (buffer, data) {
           buffer.addAll(data);
           return buffer;
         })
         .then((data) {
           Expect.listEquals(expected, data);
           port.close();
         });
     controller.add(data);
     controller.close();
   }
@@ skipping 19 matching lines @@
            255, 255]);
   test(9, [120, 218, 98, 96, 100, 98, 102, 97, 101, 99, 231, 224, 4, 0, 0, 0,
            255, 255]);
 }
 
 
 void testZLibDeflateEmpty() {
   var port = new ReceivePort();
   var controller = new StreamController();
   controller.stream.transform(new ZLibDeflater(gzip: false, level: 6))
-      .reduce([], (buffer, data) {
+      .fold([], (buffer, data) {
         buffer.addAll(data);
         return buffer;
       })
       .then((data) {
         print(data);
         Expect.listEquals([120, 156, 2, 0, 0, 0, 255, 255], data);
         port.close();
       });
   controller.close();
 }
 
 
 void testZLibDeflateGZip() {
   var port = new ReceivePort();
   var data = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
   var controller = new StreamController();
   controller.stream.transform(new ZLibDeflater())
-      .reduce([], (buffer, data) {
+      .fold([], (buffer, data) {
         buffer.addAll(data);
         return buffer;
       })
       .then((data) {
         Expect.equals(26, data.length);
         Expect.listEquals([98, 96, 100, 98, 102, 97, 101, 99, 231, 224, 4, 0, 0,
                            0, 255, 255],
                           // Skip header, as it can change.
                           data.sublist(10));
         port.close();
@@ skipping 25 matching lines @@
 }
 
 void testZLibInflate() {
   test2(bool gzip, int level) {
     var port = new ReceivePort();
     var data = [0, 1, 2, 3, 4, 5, 6, 7, 8, 9];
     var controller = new StreamController();
     controller.stream
       .transform(new ZLibDeflater(gzip: gzip, level: level))
       .transform(new ZLibInflater())
-        .reduce([], (buffer, data) {
+        .fold([], (buffer, data) {
           buffer.addAll(data);
           return buffer;
         })
         .then((inflated) {
           Expect.listEquals(data, inflated);
           port.close();
         });
     controller.add(data);
     controller.close();
   }
   void test(int level) {
     test2(false, level);
     test2(true, level);
   }
   for (int i = -1; i < 10; i++) {
     test(i);
   }
 }
 
 void main() {
   testZLibDeflate();
   testZLibDeflateEmpty();
   testZLibDeflateGZip();
   testZLibDeflateInvalidLevel();
   testZLibInflate();
 }