Persist Directory to disk when the app is backgrounded.

chrome/browser/sync/profile_sync_service.cc

 // 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.
 
 #include "chrome/browser/sync/profile_sync_service.h"
 
 #include <cstddef>
 #include <map>
 #include <vector>
 
@@ skipping 2749 matching lines @@
                  true));
 }
 
 bool ProfileSyncService::NeedBackup() const {
   return need_backup_;
 }
 
 base::Time ProfileSyncService::GetDeviceBackupTimeForTesting() const {
   return backend_->GetSyncedDeviceTracker()->GetLocalDeviceBackupTime();
 }
+
+void ProfileSyncService::FlushDirectory() const {
+  // If the user is signed out of sync, backend can be NULL.
+  if (backend_ != NULL) {
+    backend_->FlushDirectory();
+  }
+}