message: Convert one more string to string_view.
diff: @@ -1159,7 +1159,8 @@ Status DeadnessAnalysisImpl::GetFrameBasedTopologicalOrder(
  // ready_enters_per_frame and ready_exits serve as a staging area to buffer
  // the ready enters/exits before they are moved to the `ready` queue for
  // controlling the start and end of a processing frame.
  - absl::flat_hash_map<string, std::vector<Node*>> ready_enters_per_frame;
  + absl::flat_hash_map<absl::string_view, std::vector<Node*>>
  + ready_enters_per_frame;
  // Exit nodes shall all be from the same frame, as we process a frame at a
  // time. So, one vector is enough.
  std::vector<Node*> ready_exits;
  