message: Replace iter->second with partition_graph in DirectSession::Run
  This loop uses an iterator. It takes references to iter->first and iter->second right at the top of the loop and uses these references throughout, except for this line, which I've fixed.
diff: @@ -1228,7 +1228,7 @@ Status DirectSession::CreateExecutors(
  }
  };
  - optimizer.Optimize(lib, options_.env, device, &iter->second,
  + optimizer.Optimize(lib, options_.env, device, &partition_graph,
  /*shape_map=*/nullptr);
  // TensorFlow Debugger (tfdbg) inserts debug nodes in the graph.
  