Add BackupRollbackController for starting backup/rollback

chrome/common/chrome_switches.cc

Index: chrome/common/chrome_switches.cc
diff --git a/chrome/common/chrome_switches.cc b/chrome/common/chrome_switches.cc
index 8395a22a530cfe017862ad0d074d4e09fdab2dad..f1bf5010d92e145c4ff1b14490812b4e80eeca7e 100644
--- a/chrome/common/chrome_switches.cc
+++ b/chrome/common/chrome_switches.cc
@@ -1257,6 +1257,9 @@ const char kSyncEnableGetUpdateAvoidance[]   =
 const char kSyncfsEnableDirectoryOperation[] =
     "enable-syncfs-directory-operation";
 
+// Enables backup/rollback of user's data.
+const char kSyncEnableBackupRollback[] = "enable-sync-backup-rollback";
+
 // Passes the name of the current running automated test to Chrome.
 const char kTestName[]                      = "test-name";