Fix non-noise cpplint errors in //crypto.

crypto/scoped_test_system_nss_key_slot.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_SYSTEM_NSS_KEY_SLOT_H_
 #define CRYPTO_SCOPED_TEST_SYSTEM_NSS_KEY_SLOT_H_
 
 #include <memory>
 
 #include "base/macros.h"
 #include "crypto/crypto_export.h"
 
 // Forward declaration, from <pk11pub.h>
 typedef struct PK11SlotInfoStr PK11SlotInfo;
 
 namespace crypto {
 
 class ScopedTestNSSDB;
 
 // Opens a persistent NSS software database in a temporary directory and sets
 // the test system slot to the opened database. This helper should be created in
 // tests to fake the system token that is usually provided by the Chaps module.
 // |slot| is exposed through |GetSystemNSSKeySlot| and |IsTPMTokenReady| will
 // return true.
 // |InitializeTPMTokenAndSystemSlot|, which triggers the TPM initialization,
 // does not have to be called if this helper is used.
 // At most one instance of this helper must be used at a time.
 class CRYPTO_EXPORT ScopedTestSystemNSSKeySlot {
  public:
-  explicit ScopedTestSystemNSSKeySlot();
+  ScopedTestSystemNSSKeySlot();
   ~ScopedTestSystemNSSKeySlot();
 
   bool ConstructedSuccessfully() const;
   PK11SlotInfo* slot() const;
 
  private:
   std::unique_ptr<ScopedTestNSSDB> test_db_;
 
   DISALLOW_COPY_AND_ASSIGN(ScopedTestSystemNSSKeySlot);
 };
 
 }  // namespace crypto
 
 #endif  // CRYPTO_SCOPED_TEST_SYSTEM_NSS_KEY_SLOT_H_