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

tests/standalone/io/http_proxy_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:uri";
 
 class Server {
   HttpServer server;
@@ skipping 10 matching lines @@
         ? HttpServer.bindSecure(
             "127.0.0.1", 0, certificateName: 'localhost_cert')
         : HttpServer.bind();
     return f.then((s) {
       server = s;
       x.complete(this);
       server.listen((request) {
         var response = request.response;
         requestCount++;
         // Check whether a proxy or direct connection is expected.
-        bool direct = directRequestPaths.reduce(
+        bool direct = directRequestPaths.fold(
             false,
             (prev, path) => prev ? prev : path == request.uri.path);
         if (!direct && proxyHops > 0) {
           Expect.isNotNull(request.headers[HttpHeaders.VIA]);
           Expect.equals(1, request.headers[HttpHeaders.VIA].length);
           Expect.equals(
               proxyHops,
               request.headers[HttpHeaders.VIA][0].split(",").length);
         } else {
           Expect.isNull(request.headers[HttpHeaders.VIA]);
@@ skipping 370 matching lines @@
   InitializeSSL();
   testInvalidProxy();
   testDirectProxy();
   testProxy();
   testProxyChain();
   testProxyFromEnviroment();
   // This test is not normally run. It can be used for locally testing
   // with a real proxy server (e.g. Apache).
   //testRealProxy();
 }