Adds a new checkbox for backup and restore in opt-in flow.

chrome/common/pref_names.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.
 
 // Constants for the names of various preferences, for easier changing.
 
 #ifndef CHROME_COMMON_PREF_NAMES_H_
 #define CHROME_COMMON_PREF_NAMES_H_
 
 #include <stddef.h>
 
 #include "build/build_config.h"
 #include "chrome/common/features.h"
 
 namespace prefs {
 
 // Profile prefs. Please add Local State prefs below instead.
 #if defined(OS_CHROMEOS) && defined(ENABLE_APP_LIST)
 extern const char kArcApps[];
+extern const char kArcBackupRestoreEnabled[];
 extern const char kArcEnabled[];
 extern const char kArcPackages[];
 extern const char kArcSetNotificationsEnabledDeferred[];
 extern const char kArcSignedIn[];
 #endif
 extern const char kChildAccountStatusKnown[];
 extern const char kDefaultApps[];
 extern const char kDisableScreenshots[];
 extern const char kForceEphemeralProfiles[];
 extern const char kHomePageIsNewTabPage[];
@@ skipping 787 matching lines @@
 #endif  // defined(GOOGLE_CHROME_BUILD)
 extern const char kMediaRouterFirstRunFlowAcknowledged[];
 #endif
 
 extern const char kOriginTrialPublicKey[];
 extern const char kOriginTrialDisabledFeatures[];
 
 }  // namespace prefs
 
 #endif  // CHROME_COMMON_PREF_NAMES_H_