Copy some x509_certificate_model_nss functions to src/chromeos (reland)

chrome/browser/chromeos/options/cert_library.h

Index: chrome/browser/chromeos/options/cert_library.h
diff --git a/chrome/browser/chromeos/options/cert_library.h b/chrome/browser/chromeos/options/cert_library.h
index cc5a6f27b1db963cfa2973d6629802c8e78192e5..65b3bc0258896395db562223c3fe903121d8ded1 100644
--- a/chrome/browser/chromeos/options/cert_library.h
+++ b/chrome/browser/chromeos/options/cert_library.h
@@ -9,6 +9,7 @@
 
 #include "base/macros.h"
 #include "base/strings/string16.h"
+#include "base/threading/thread_checker.h"
 #include "chromeos/cert_loader.h"
 #include "net/cert/x509_certificate.h"
 
@@ -96,6 +97,8 @@ class CertLibrary : public CertLoader::Observer {
   net::CertificateList server_certs_;
   net::CertificateList server_ca_certs_;
 
+  THREAD_CHECKER(thread_checker_);
+
   DISALLOW_COPY_AND_ASSIGN(CertLibrary);
 };