Fix non-noise cpplint errors in //crypto.

crypto/nss_util_internal.h

 // Copyright (c) 2012 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_NSS_UTIL_INTERNAL_H_
 #define CRYPTO_NSS_UTIL_INTERNAL_H_
 
 #include <secmodt.h>
 
+#include <string>
+
 #include "base/callback.h"
 #include "base/compiler_specific.h"
 #include "base/macros.h"
 #include "crypto/crypto_export.h"
 #include "crypto/scoped_nss_types.h"
 
 namespace base {
 class FilePath;
 }
 
@@ skipping 84 matching lines @@
 
 // Closes the NSS DB for |username_hash| that was previously opened by the
 // *Initialize*ForChromeOSUser functions.
 CRYPTO_EXPORT void CloseChromeOSUserForTesting(
     const std::string& username_hash);
 #endif  // defined(OS_CHROMEOS)
 
 }  // namespace crypto
 
 #endif  // CRYPTO_NSS_UTIL_INTERNAL_H_