Use sockets with unread data if they've never been used before.

net/socket/socks_client_socket.h

Index: net/socket/socks_client_socket.h
diff --git a/net/socket/socks_client_socket.h b/net/socket/socks_client_socket.h
index d4f058a62b1a2af831a072b5cfed7e00b8a3614d..be05ce0fad0804a5a2930c4ecb1c3a879f6edf61 100644
--- a/net/socket/socks_client_socket.h
+++ b/net/socket/socks_client_socket.h
@@ -84,6 +84,7 @@ class NET_EXPORT_PRIVATE SOCKSClientSocket : public StreamSocket {
 
   void DoCallback(int result);
   void OnIOComplete(int result);
+  void OnReadWriteComplete(const CompletionCallback& callback, int result);
 
   int DoLoop(int last_io_result);
   int DoResolveHost();
@@ -100,7 +101,7 @@ class NET_EXPORT_PRIVATE SOCKSClientSocket : public StreamSocket {
 
   State next_state_;
 
-  // Stores the callback to the layer above, called on completing Connect().
+  // Stores the callbacks to the layer above, called on completing Connect().
   CompletionCallback user_callback_;
 
   // This IOBuffer is used by the class to read and write
@@ -120,6 +121,9 @@ class NET_EXPORT_PRIVATE SOCKSClientSocket : public StreamSocket {
   size_t bytes_sent_;
   size_t bytes_received_;
 
+  // This becomes true when the socket is used to send or receive data.
+  bool was_ever_used_;
+
   // Used to resolve the hostname to which the SOCKS proxy will connect.
   SingleRequestHostResolver host_resolver_;
   AddressList addresses_;