[Sync] Allow sync start without sign-in if the local sync backend is on.

components/sync/driver/sync_service_base.cc

 // Copyright 2016 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/driver/sync_service_base.h"
 
 #include <utility>
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
@@ skipping 118 matching lines @@
         base::PathService::Get(base::DIR_APP_DATA, local_sync_backend_folder));
     *local_sync_backend_folder = local_sync_backend_folder->Append(
         FILE_PATH_LITERAL("Chrome/User Data"));
   }
   // This code as it is now will assume the same profile order is present on all
   // machines, which is not a given. It is to be defined if only the Default
   // profile should get this treatment or all profile as is the case now. The
   // solution for now will be to assume profiles are created in the same order
   // on all machines and in the future decide if only the Default one should be
   // considered roamed.
+  // See http://crbug.com/674928.
   *local_sync_backend_folder =
       local_sync_backend_folder->Append(base_directory_.BaseName());
   *local_sync_backend_folder =
       local_sync_backend_folder->Append(kLoopbackServerBackendFilename);
 #endif  // defined(OS_WIN)
   return enable_local_sync_backend;
 }
 
 }  // namespace syncer