Avoid doing concurrent DNS resolves of the same hostname

net/http/http_network_layer.h

Index: net/http/http_network_layer.h
===================================================================
--- net/http/http_network_layer.h	(revision 18213)
+++ net/http/http_network_layer.h	(working copy)
@@ -11,14 +11,16 @@
 
 namespace net {
 
+class HostResolver;
 class HttpNetworkSession;
 class ProxyInfo;
 class ProxyService;
 
 class HttpNetworkLayer : public HttpTransactionFactory {
  public:
-  // |proxy_service| must remain valid for the lifetime of HttpNetworkLayer.
-  explicit HttpNetworkLayer(ProxyService* proxy_service);
+  // |proxy_service| and |host_resolver| must remain valid for the lifetime of
+  // HttpNetworkLayer.
+  HttpNetworkLayer(HostResolver* host_resolver, ProxyService* proxy_service);
   // Construct a HttpNetworkLayer with an existing HttpNetworkSession which
   // contains a valid ProxyService.
   explicit HttpNetworkLayer(HttpNetworkSession* session);
@@ -26,7 +28,8 @@
 
   // This function hides the details of how a network layer gets instantiated
   // and allows other implementations to be substituted.
-  static HttpTransactionFactory* CreateFactory(ProxyService* proxy_service);
+  static HttpTransactionFactory* CreateFactory(HostResolver* host_resolver,
+                                               ProxyService* proxy_service);
   // Create a transaction factory that instantiate a network layer over an
   // existing network session. Network session contains some valuable
   // information (e.g. authentication data) that we want to share across
@@ -43,6 +46,9 @@
   HttpNetworkSession* GetSession();
 
  private:
+  // The host resolver being used for the session.
+  HostResolver* host_resolver_;
+
   // The proxy service being used for the session.
   ProxyService* proxy_service_;