experiment with -Wimplicit-fallthrough

net/cert/cert_database_mac.cc

 // 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.
 
 #include "net/cert/cert_database.h"
 
 #include <Security/Security.h>
 
 #include "base/logging.h"
 #include "base/mac/mac_logging.h"
@@ skipping 141 matching lines @@
 
 int CertDatabase::AddUserCert(X509Certificate* cert) {
   OSStatus err;
   {
     base::AutoLock locked(crypto::GetMacSecurityServicesLock());
     err = SecCertificateAddToKeychain(cert->os_cert_handle(), NULL);
   }
   switch (err) {
     case noErr:
       CertDatabase::NotifyObserversOfCertAdded(cert);
-      // Fall through.
+      FALLTHROUGH_INTENDED;
     case errSecDuplicateItem:
       return OK;
     default:
       OSSTATUS_LOG(ERROR, err) << "CertDatabase failed to add cert to keychain";
       // TODO(snej): Map the error code more intelligently.
       return ERR_ADD_USER_CERT_FAILED;
   }
 }
 
 }  // namespace net