message: Add default values of attributes that might have been stripped by
  optimizations.
diff: @@ -135,7 +135,10 @@ Status OptimizeGraph(const GraphDef& graph_def_arg, GraphDef* output_graph_def,
  optimizer.Optimize(flr, env, devices[0], &graphptr, /*shape_map=*/nullptr);
  graphptr->ToGraphDef(output_graph_def);
  - return Status::OK();
  + // The default values of attributes might have been stripped by the optimizer.
  + // Add them back.
  + return AddDefaultAttrsToGraphDef(output_graph_def, *graphptr->op_registry(),
  + 0);
  }
  // Applies the same graph pruning logic to the graph as Session.Run in TF.
  @@ -446,7 +449,7 @@ std::unique_ptr<GrapplerItem> GrapplerItemFromMetaGraphDef(
  new_item->save_restore_loc_tensor = saver.filename_tensor_name();
  }
  - // Populate default attrs to the NodeDefs in the GraphDef.
  + // Instantiate all the missing attributes with their default values.
  Status attr_status =
  AddDefaultAttrsToGraphDef(&new_item->graph, *OpRegistry::Global(), 0);
  if (!attr_status.ok()) {
  