message: Fix -Wunused-variable error.
  Cr-Commit-Position: refs/heads/master@{#31450}
diff: @@ -33,11 +33,9 @@ class PerfTestData {
  int64_t my_counter_ = 0;
  };
  -// TODO(bugs.webrtc.org/11630): remove NOLINT when linter supports mutable
  -// references.
  -void BM_LockWithMutex(benchmark::State& state) { // NOLINT
  +void BM_LockWithMutex(benchmark::State& state) {
  static PerfTestData test_data;
  - for (auto s : state) {
  + for (auto it = state.begin(); it != state.end(); ++it) {
  benchmark::DoNotOptimize(test_data.AddToCounter(2));
  }
  }
  