message: [Grappler] Save another graph copy in constant folding.
diff: @@ -3766,7 +3766,8 @@ Status ConstantFolding::Optimize(Cluster* cluster, const GrapplerItem& item,
  has_fetch_ = !item.fetch.empty();
  GrapplerItem item_to_optimize = item;
  - *optimized_graph = item.graph;
  + *optimized_graph = GraphDef();
  + item_to_optimize.graph.Swap(optimized_graph);
  int64 node_count;
  do {
  GRAPPLER_RETURN_IF_DEADLINE_EXCEEDED();
  