Persist Directory to disk when the app is backgrounded.

chrome/browser/sync/profile_sync_service.cc

Index: chrome/browser/sync/profile_sync_service.cc
diff --git a/chrome/browser/sync/profile_sync_service.cc b/chrome/browser/sync/profile_sync_service.cc
index cb699d83b8c6b46e8198232b648433a13aab2d35..eb76001e7fd1e646b9f9bdb514b4ec0be0d7a5b2 100644
--- a/chrome/browser/sync/profile_sync_service.cc
+++ b/chrome/browser/sync/profile_sync_service.cc
@@ -2707,3 +2707,10 @@ bool ProfileSyncService::NeedBackup() const {
 base::Time ProfileSyncService::GetDeviceBackupTimeForTesting() const {
   return device_info_sync_service_->GetLocalDeviceBackupTime();
 }
+
+void ProfileSyncService::FlushDirectory() const {
+  // backend_initialized_ implies backend_ isn't NULL and the manager exists.
+  // If sync is not initialized yet, we fail silently.
+  if (backend_initialized_)
+    backend_->FlushDirectory();
+}