Remove some dead code about "acknowledged types"

components/sync_driver/pref_names.cc

 // 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.
 
 #include "components/sync_driver/pref_names.h"
 
 namespace sync_driver {
 
 namespace prefs {
 
@@ skipping 68 matching lines @@
 
 // Same as kSyncEncryptionBootstrapToken, but derived from the keystore key,
 // so we don't have to do a GetKey command at restart.
 const char kSyncKeystoreEncryptionBootstrapToken[] =
     "sync.keystore_encryption_bootstrap_token";
 
 // Boolean tracking whether the user chose to specify a secondary encryption
 // passphrase.
 const char kSyncUsingSecondaryPassphrase[] = "sync.using_secondary_passphrase";
 
-// List of the currently acknowledged set of sync types, used to figure out
-// if a new sync type has rolled out so we can notify the user.
-const char kSyncAcknowledgedSyncTypes[] = "sync.acknowledged_types";
-
 // The GUID session sync will use to identify this client, even across sync
 // disable/enable events.
 const char kSyncSessionsGUID[] = "sync.session_sync_guid";
 
 #if defined(OS_CHROMEOS)
 // A string that is used to store first-time sync startup after once sync is
 // disabled. This will be refreshed every sign-in.
 const char kSyncSpareBootstrapToken[] = "sync.spare_bootstrap_token";
 #endif  // defined(OS_CHROMEOS)
 
 // Stores how many times to try rollback before giving up.
 const char kSyncRemainingRollbackTries[] = "sync.remaining_rollback_tries";
 
 // Stores the timestamp of first sync.
 const char kSyncFirstSyncTime[] = "sync.first_sync_time";
 
 }  // namespace prefs
 
 }  // namespace sync_driver