Avoid doing concurrent DNS resolves of the same hostname

net/base/tcp_client_socket_pool.h

Index: net/base/tcp_client_socket_pool.h
===================================================================
--- net/base/tcp_client_socket_pool.h	(revision 18213)
+++ net/base/tcp_client_socket_pool.h	(working copy)
@@ -25,6 +25,7 @@
 class TCPClientSocketPool : public ClientSocketPool {
  public:
   TCPClientSocketPool(int max_sockets_per_group,
+                      HostResolver* host_resolver,
                       ClientSocketFactory* client_socket_factory);
 
   // ClientSocketPool methods:
@@ -44,6 +45,10 @@
 
   virtual void CloseIdleSockets();
 
+  virtual HostResolver* GetHostResolver() const {
+    return host_resolver_;
+  }
+
   virtual int idle_socket_count() const {
     return idle_socket_count_;
   }
@@ -137,7 +142,7 @@
     CompletionCallbackImpl<ConnectingSocket> callback_;
     scoped_ptr<ClientSocket> socket_;
     scoped_refptr<TCPClientSocketPool> pool_;
-    HostResolver resolver_;
+    SingleRequestHostResolver resolver_;
     AddressList addresses_;
     bool canceled_;
 
@@ -185,6 +190,10 @@
   // The maximum number of sockets kept per group.
   const int max_sockets_per_group_;
 
+  // The host resolver that will be used to do DNS lookups for connecting
+  // sockets.
+  HostResolver* host_resolver_;
+
   DISALLOW_COPY_AND_ASSIGN(TCPClientSocketPool);
 };