[Sync] Stop accessing BrowserContextKeyedServiceFactory on non-UI thread.

components/sync/driver/directory_data_type_controller.cc

Index: components/sync/driver/directory_data_type_controller.cc
diff --git a/components/sync/driver/directory_data_type_controller.cc b/components/sync/driver/directory_data_type_controller.cc
index a03ee3dd17c026ff9ef07a88933505883b7e9674..8ae2d034ebec9ed875cdfde2e50dce28f6527079 100644
--- a/components/sync/driver/directory_data_type_controller.cc
+++ b/components/sync/driver/directory_data_type_controller.cc
@@ -62,6 +62,7 @@ void DirectoryDataTypeController::DeactivateDataType(
 
 void DirectoryDataTypeController::GetAllNodes(
     const AllNodesCallback& callback) {
+  DCHECK(CalledOnValidThread());
   std::unique_ptr<base::ListValue> node_list = GetAllNodesForTypeFromDirectory(
       type(), sync_client_->GetSyncService()->GetUserShare()->directory.get());
   callback.Run(type(), std::move(node_list));
@@ -69,6 +70,7 @@ void DirectoryDataTypeController::GetAllNodes(
 
 void DirectoryDataTypeController::GetStatusCounters(
     const StatusCountersCallback& callback) {
+  DCHECK(CalledOnValidThread());
   std::vector<int> num_entries_by_type(syncer::MODEL_TYPE_COUNT, 0);
   std::vector<int> num_to_delete_entries_by_type(syncer::MODEL_TYPE_COUNT, 0);
   sync_client_->GetSyncService()