Define a single macro for enabling backup function.

chrome/browser/sync/backup_rollback_controller.cc

Index: chrome/browser/sync/backup_rollback_controller.cc
diff --git a/chrome/browser/sync/backup_rollback_controller.cc b/chrome/browser/sync/backup_rollback_controller.cc
index 1f0de17a67bb9bd42bfb8ef35788a9cf7512401c..c7018e3953575cadffe62b0058abe3cf87336fd5 100644
--- a/chrome/browser/sync/backup_rollback_controller.cc
+++ b/chrome/browser/sync/backup_rollback_controller.cc
@@ -12,7 +12,7 @@
 
 namespace browser_sync {
 
-#if defined(OS_WIN) || defined(OS_MACOSX) || (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+#if defined(ENABLE_PRE_SYNC_BACKUP)
 // Number of rollback attempts to try before giving up.
 static const int kRollbackLimits = 3;
 #endif
@@ -33,7 +33,7 @@ BackupRollbackController::~BackupRollbackController() {
 }
 
 void BackupRollbackController::Start(base::TimeDelta delay) {
-#if defined(OS_WIN) || defined(OS_MACOSX) || (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+#if defined(ENABLE_PRE_SYNC_BACKUP)
   if (CommandLine::ForCurrentProcess()->HasSwitch(
           switches::kSyncDisableBackup)) {
     return;
@@ -57,13 +57,13 @@ void BackupRollbackController::Start(base::TimeDelta delay) {
 }
 
 void BackupRollbackController::OnRollbackReceived() {
-#if defined(OS_WIN) || defined(OS_MACOSX) || (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+#if defined(ENABLE_PRE_SYNC_BACKUP)
   sync_prefs_->SetRemainingRollbackTries(kRollbackLimits);
 #endif
 }
 
 void BackupRollbackController::OnRollbackDone() {
-#if defined(OS_WIN) || defined(OS_MACOSX) || (defined(OS_LINUX) && !defined(OS_CHROMEOS))
+#if defined(ENABLE_PRE_SYNC_BACKUP)
   sync_prefs_->SetRemainingRollbackTries(0);
 #endif
 }