message: Enable saved model restoration using just a .pb file.
diff: @@ -404,10 +404,12 @@ Status RestoreSession(const RunOptions& run_options,
  const uint64 read_start_microseconds = Env::Default()->NowMicros();
  std::vector<AssetFileDef> asset_file_defs;
  TF_RETURN_IF_ERROR(internal::GetAssetFileDefs(meta_graph, &asset_file_defs));
  + if (meta_graph.has_saver_def()) {
  TF_RETURN_IF_ERROR(RunRestore(run_options, export_dir,
  meta_graph.saver_def().restore_op_name(),
  meta_graph.saver_def().filename_tensor_name(),
  asset_file_defs, session->get()));
  + }
  // Record walltime spent in restoring graph from disk, but postpone metric
  // increments until graph init finishes.
  const uint64 restore_graph_walltime =
  