net: plumb DnsRRResolver from IOThread to HttpNetworkSession.

net/url_request/url_request_context.cc

 // Copyright (c) 2010 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/url_request/url_request_context.h"
 
 #include "base/string_util.h"
 #include "net/base/cookie_store.h"
 #include "net/base/host_resolver.h"
 
 URLRequestContext::URLRequestContext()
     : net_log_(NULL),
+      dnsrr_resolver_(NULL),
       http_transaction_factory_(NULL),
       ftp_transaction_factory_(NULL),
       http_auth_handler_factory_(NULL),
       network_delegate_(NULL),
       cookie_policy_(NULL),
       transport_security_state_(NULL) {
 }
 
 const std::string& URLRequestContext::GetUserAgent(const GURL& url) const {
   return EmptyString();
 }
 
 URLRequestContext::~URLRequestContext() {
 }