Refactor how ClientSocketPoolBaseHelper avoids re-entrancy.

net/http/http_network_transaction_unittest.cc

Index: net/http/http_network_transaction_unittest.cc
diff --git a/net/http/http_network_transaction_unittest.cc b/net/http/http_network_transaction_unittest.cc
index 48945db7952d3b80fadd0e8c307cd5006811ba4b..c21634ff239fb88c95a790e1c9e68a94ccfe78ee 100644
--- a/net/http/http_network_transaction_unittest.cc
+++ b/net/http/http_network_transaction_unittest.cc
@@ -267,7 +267,7 @@ class CaptureGroupNameSocketPool : public ParentPool {
     return ERR_IO_PENDING;
   }
   virtual void CancelRequest(const std::string& group_name,
-                             const ClientSocketHandle* handle) { }
+                             ClientSocketHandle* handle) {}
   virtual void ReleaseSocket(const std::string& group_name,
                              ClientSocket* socket) {}
   virtual void CloseIdleSockets() {}