Make the proxy server HostPortPair available in document_state so that

content/public/common/resource_response_info.h

 // Copyright 2014 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.
 
 #ifndef CONTENT_PUBLIC_COMMON_RESOURCE_RESPONSE_INFO_H_
 #define CONTENT_PUBLIC_COMMON_RESOURCE_RESPONSE_INFO_H_
 
 #include <string>
 
 #include "base/basictypes.h"
@@ skipping 76 matching lines @@
   bool was_alternate_protocol_available;
 
   // Information about the type of connection used to fetch this response.
   net::HttpResponseInfo::ConnectionInfo connection_info;
 
   // True if the response was fetched via an explicit proxy (as opposed to a
   // transparent proxy). The proxy could be any type of proxy, HTTP or SOCKS.
   // Note: we cannot tell if a transparent proxy may have been involved.
   bool was_fetched_via_proxy;
 
+  // Remote address of the proxy server used for this resource, if one was used.
+  net::HostPortPair proxy_server;

[Charlie Reis, 2014/10/30 18:05:32]

It wasn't clear to me whether we need both this and |was_fetched_via_proxy|. 
Looks like they're grouped together with a comment in HttpResponseInfo.  Can we
do something similar here?

[jeremyim, 2014/10/30 19:00:36]

Done.

+
   // NPN protocol negotiated with the server.
   std::string npn_negotiated_protocol;
 
   // Remote address of the socket which fetched this resource.
   net::HostPortPair socket_address;
 
   // True if the response was fetched by a ServiceWorker.
   bool was_fetched_via_service_worker;
 
   // True when the request whoes mode is |CORS| or |CORS-with-forced-preflight|
@@ skipping 12 matching lines @@
   // ServiceWorker Timing Information. These will be set if the response is
   // provided by the ServiceWorker, or kept empty.
   base::TimeTicks service_worker_fetch_start;
   base::TimeTicks service_worker_fetch_ready;
   base::TimeTicks service_worker_fetch_end;
 };
 
 }  // namespace content
 
 #endif  // CONTENT_PUBLIC_COMMON_RESOURCE_RESPONSE_INFO_H_