Enable system NSS key slot.

crypto/scoped_test_nss_db.h

 // Copyright 2014 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 CRYPTO_SCOPED_TEST_NSS_DB_H_
 #define CRYPTO_SCOPED_TEST_NSS_DB_H_
 
 #include "base/files/scoped_temp_dir.h"
 #include "base/macros.h"
 #include "crypto/crypto_export.h"
 #include "crypto/scoped_nss_types.h"
 
 namespace crypto {
 
 // Opens a persistent NSS database in a temporary directory.
 // Prior NSS version 3.15.1, because of http://bugzil.la/875601 , the opened DB
 // will not be closed automatically.
 class CRYPTO_EXPORT_PRIVATE ScopedTestNSSDB {
  public:
   ScopedTestNSSDB();
   ~ScopedTestNSSDB();
 
-  bool is_open() { return slot_; }
-  PK11SlotInfo* slot() { return slot_.get(); }
+  bool is_open() const { return slot_; }
+  PK11SlotInfo* slot() const { return slot_.get(); }
 
  private:
   base::ScopedTempDir temp_dir_;
   ScopedPK11Slot slot_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedTestNSSDB);
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_SCOPED_TEST_NSS_DB_H_