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

tests/standalone/io/http_auth_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:crypto';
 import 'dart:io';
 import 'dart:isolate';
 import 'dart:uri';
 import 'dart:utf';
@@ skipping 80 matching lines @@
 
 void testBasicNoCredentials() {
   setupServer().then((server) {
     HttpClient client = new HttpClient();
 
     Future makeRequest(Uri url) {
       return client.getUrl(url)
         .then((HttpClientRequest request) => request.close())
         .then((HttpClientResponse response) {
           Expect.equals(HttpStatus.UNAUTHORIZED, response.statusCode);
-          return response.reduce(null, (x, y) {});
+          return response.fold(null, (x, y) {});
         });
     }
 
     var futures = [];
     for (int i = 0; i < 5; i++) {
       futures.add(
           makeRequest(
               Uri.parse("http://127.0.0.1:${server.port}/test$i")));
       futures.add(
           makeRequest(
               Uri.parse(
                   "http://127.0.0.1:${server.port}/test$i/xxx")));
     }
     Future.wait(futures).then((_) {
       server.shutdown();
       client.close();
     });
   });
 }
 
 void testBasicCredentials() {
   setupServer().then((server) {
     HttpClient client = new HttpClient();
 
     Future makeRequest(Uri url) {
       return client.getUrl(url)
         .then((HttpClientRequest request) => request.close())
         .then((HttpClientResponse response) {
           Expect.equals(HttpStatus.OK, response.statusCode);
-          return response.reduce(null, (x, y) {});
+          return response.fold(null, (x, y) {});
         });
     }
 
     for (int i = 0; i < 5; i++) {
       client.addCredentials(
           Uri.parse("http://127.0.0.1:${server.port}/test$i"),
           "realm",
           new HttpClientBasicCredentials("test$i", "test$i"));
     }
 
@@ skipping 32 matching lines @@
         completer.complete(true);
       });
       return completer.future;
     };
 
     Future makeRequest(Uri url) {
       return client.getUrl(url)
         .then((HttpClientRequest request) => request.close())
         .then((HttpClientResponse response) {
           Expect.equals(HttpStatus.OK, response.statusCode);
-          return response.reduce(null, (x, y) {});
+          return response.fold(null, (x, y) {});
         });
     }
 
     List<Future> makeRequests() {
       var futures = [];
       for (int i = 0; i < 5; i++) {
         futures.add(
             makeRequest(
                 Uri.parse("http://127.0.0.1:${server.port}/test$i")));
         futures.add(
@@ skipping 64 matching lines @@
 main() {
   testUrlUserInfo();
   testBasicNoCredentials();
   testBasicCredentials();
   testBasicAuthenticateCallback();
   // These teste are not normally run. They can be used for locally
   // testing with another web server (e.g. Apache).
   //testLocalServerBasic();
   //testLocalServerDigest();
 }