When using SSLClientSocketNSS on Windows, fall back on SSLClientSocketWin...

net/socket/ssl_client_socket_nss.h

 // Copyright (c) 2006-2009 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_SOCKET_SSL_CLIENT_SOCKET_NSS_H_
 #define NET_SOCKET_SSL_CLIENT_SOCKET_NSS_H_
 
 #include <certt.h>
 #include <keyt.h>
 #include <nspr.h>
@@ skipping 139 matching lines @@
 
   // The NSS SSL state machine
   PRFileDesc* nss_fd_;
 
   // Buffers for the network end of the SSL state machine
   memio_Private* nss_bufs_;
 
   scoped_refptr<LoadLog> load_log_;
 
 #if defined(OS_WIN)
-  // A CryptoAPI in-memory certificate store that we import server
-  // certificates into so that we can verify and display the certificates
-  // using CryptoAPI.
+  // A CryptoAPI in-memory certificate store.  We use it for two purposes:
+  // 1. Import server certificates into this store so that we can verify and
+  //    display the certificates using CryptoAPI.
+  // 2. Copy client certificates from the "MY" system certificate store into
+  //    this store so that we can close the system store when we finish
+  //    searching for client certificates.
   static HCERTSTORE cert_store_;
 #endif
 };
 
 }  // namespace net
 
 #endif  // NET_SOCKET_SSL_CLIENT_SOCKET_NSS_H_