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

chrome/common/pref_names.cc

Index: chrome/common/pref_names.cc
diff --git a/chrome/common/pref_names.cc b/chrome/common/pref_names.cc
index f9e1dc2d20440eb19576ef5ad0636b58a0828a58..5307ce393384dd5f32cfae4ed1b1f8e4a767be5b 100644
--- a/chrome/common/pref_names.cc
+++ b/chrome/common/pref_names.cc
@@ -16,6 +16,8 @@ namespace prefs {
 #if defined(OS_CHROMEOS) && defined(ENABLE_APP_LIST)
 // A preference to keep list of Android apps and their state.
 const char kArcApps[] = "arc.apps";
+// A preference to store backup and restore state for Android apps.
+const char kArcBackupRestoreEnabled[] = "arc.backup_restore.enabled";
 // A preference to keep Android apps enabled state.
 const char kArcEnabled[] = "arc.enabled";
 // A preference to keep list of Android packages and their infomation.