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

components/sync/engine/sync_manager.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 "components/sync/engine/sync_manager.h"
 
 namespace syncer {
 
 SyncCredentials::SyncCredentials() {}
 
 SyncCredentials::SyncCredentials(const SyncCredentials& other) = default;
 
 SyncCredentials::~SyncCredentials() {}
 
 SyncManager::ChangeDelegate::~ChangeDelegate() {}
 
 SyncManager::ChangeObserver::~ChangeObserver() {}
 
 SyncManager::Observer::~Observer() {}
 
 SyncManager::InitArgs::InitArgs()
-    : extensions_activity(nullptr),
+    : enable_local_sync_backend(false),
+      extensions_activity(nullptr),
       change_delegate(nullptr),
       encryptor(nullptr),
       cancelation_signal(nullptr) {}
 
 SyncManager::InitArgs::~InitArgs() {}
 
 SyncManager::SyncManager() {}
 
 SyncManager::~SyncManager() {}
 
 }  // namespace syncer