Make the proxy server resolution from environment variables the default for HttpClient

sdk/lib/io/http_impl.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.io;
 
 class _HttpIncoming extends Stream<List<int>> {
   final int _transferLength;
   final Completer _dataCompleter = new Completer();
   Stream<List<int>> _stream;
@@ skipping 1078 matching lines @@
   // TODO(ajohnsen): Use eviction timeout.
   static const int DEFAULT_EVICTION_TIMEOUT = 60000;
   bool _closing = false;
 
   final Map<String, Queue<_HttpClientConnection>> _idleConnections
       = new Map<String, Queue<_HttpClientConnection>>();
   final Set<_HttpClientConnection> _activeConnections
       = new Set<_HttpClientConnection>();
   final List<_Credentials> _credentials = [];
   Function _authenticate;
-  Function _findProxy;
+  Function _findProxy = HttpClient.findProxyFromEnvironment;
 
   Future<HttpClientRequest> open(String method,
                                  String host,
                                  int port,
                                  String path) {
     // TODO(sgjesse): The path set here can contain both query and
     // fragment. They should be cracked and set correctly.
     return _openUrl(method, new Uri.fromComponents(
         scheme: "http", domain: host, port: port, path: path));
   }
@@ skipping 715 matching lines @@
 
 
 class _RedirectInfo implements RedirectInfo {
   const _RedirectInfo(int this.statusCode,
                       String this.method,
                       Uri this.location);
   final int statusCode;
   final String method;
   final Uri location;
 }