Revert of [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 8ae2d034ebec9ed875cdfde2e50dce28f6527079..a03ee3dd17c026ff9ef07a88933505883b7e9674 100644
--- a/components/sync/driver/directory_data_type_controller.cc
+++ b/components/sync/driver/directory_data_type_controller.cc
@@ -62,7 +62,6 @@
 
 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));
@@ -70,7 +69,6 @@
 
 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()