[Sync] Adds a new switch for enabling the new local server backend.

components/sync/engine/sync_manager.h

Index: components/sync/engine/sync_manager.h
diff --git a/components/sync/engine/sync_manager.h b/components/sync/engine/sync_manager.h
index 71bfcdc845f54d1b2fd1b2929386300cd4b1755d..6ee8e03c7dea50da69ac77329a573d7532b1a871 100644
--- a/components/sync/engine/sync_manager.h
+++ b/components/sync/engine/sync_manager.h
@@ -224,6 +224,11 @@ class SyncManager {
     // URL of the sync server.
     GURL service_url;
 
+    // Whether the local backend provided by the LoopbackServer should be used
+    // and the location of the local sync backend storage.
+    bool enable_local_sync_backend;
+    base::FilePath local_sync_backend_folder;
+
     // Used to communicate with the sync server.
     std::unique_ptr<HttpPostProviderFactory> post_factory;