[Mac] Add locking as speculative fix for X509Certificate crashes.

net/base/x509_certificate.h

 // Copyright (c) 2006-2008 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_BASE_X509_CERTIFICATE_H_
 #define NET_BASE_X509_CERTIFICATE_H_
 
 #include <string.h>
 
 #include <map>
@@ skipping 275 matching lines @@
 
   // A handle to the certificate object in the underlying crypto library.
   OSCertHandle cert_handle_;
 
 #if defined(OS_MACOSX) || defined(OS_WIN)
   // Untrusted intermediate certificates associated with this certificate
   // that may be needed for chain building. (NSS impl does not need these.)
   OSCertHandles intermediate_ca_certs_;
 #endif
 
+#if defined(OS_MACOSX)
+  // Blocks multiple threads from verifying the cert simultaneously.
+  mutable Lock lock_;

[wtc, 2010/04/27 00:06:43]

Nit: perhaps rename this lock "verify_lock_" to stress the
fact that it applies to the Verify() method only.

Nit: should we explain why this lock is mutable? (because
Verify is a const method)

+#endif
+
   // Where the certificate comes from.
   Source source_;
 
   DISALLOW_COPY_AND_ASSIGN(X509Certificate);
 };
 
 }  // namespace net
 
 #endif  // NET_BASE_X509_CERTIFICATE_H_