Avoid doing concurrent DNS resolves of the same hostname

net/http/http_network_session.h

 // Copyright (c) 2006-2008 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 NET_HTTP_HTTP_NETWORK_SESSION_H_
 #define NET_HTTP_HTTP_NETWORK_SESSION_H_
 
 #include "base/ref_counted.h"
 #include "net/base/ssl_config_service.h"
 #include "net/base/tcp_client_socket_pool.h"
 #include "net/http/http_auth_cache.h"
 
 namespace net {
 
 class ClientSocketFactory;
+class HostResolver;
 class ProxyService;
 
 // This class holds session objects used by HttpNetworkTransaction objects.
 class HttpNetworkSession : public base::RefCounted<HttpNetworkSession> {
  public:
-  HttpNetworkSession(ProxyService* proxy_service,
+  HttpNetworkSession(HostResolver* host_resolver, ProxyService* proxy_service,
                      ClientSocketFactory* client_socket_factory)
       : connection_pool_(new TCPClientSocketPool(
-            max_sockets_per_group_, client_socket_factory)),
+            max_sockets_per_group_, host_resolver, client_socket_factory)),
+        host_resolver_(host_resolver),
         proxy_service_(proxy_service) {
     DCHECK(proxy_service);
   }
 
   HttpAuthCache* auth_cache() { return &auth_cache_; }
   ClientSocketPool* connection_pool() { return connection_pool_; }
+  HostResolver* host_resolver() { return host_resolver_; }
   ProxyService* proxy_service() { return proxy_service_; }
 #if defined(OS_WIN)
   SSLConfigService* ssl_config_service() { return &ssl_config_service_; }
 #endif
 
   static void set_max_sockets_per_group(int socket_count);
 
  private:
   // Default to allow up to 6 connections per host. Experiment and tuning may
   // try other values (greater than 0).  Too large may cause many problems, such
   // as home routers blocking the connections!?!?
   static int max_sockets_per_group_;
 
   HttpAuthCache auth_cache_;
   scoped_refptr<ClientSocketPool> connection_pool_;
+  HostResolver* host_resolver_;
   ProxyService* proxy_service_;
 #if defined(OS_WIN)
   // TODO(port): Port the SSLConfigService class to Linux and Mac OS X.
   SSLConfigService ssl_config_service_;
 #endif
 };
 
 }  // namespace net
 
 #endif  // NET_HTTP_HTTP_NETWORK_SESSION_H_