message: test: avoid taking reference to temporary in access_log mocks.
  This showed up during the Google import.
diff: @@ -64,8 +64,8 @@ public:
  std::shared_ptr<testing::NiceMock<Upstream::MockHostDescription>> host_{
  new testing::NiceMock<Upstream::MockHostDescription>()};
  SystemTime start_time_;
  - std::chrono::microseconds request_received_duration_;
  - std::chrono::microseconds response_received_duration_;
  + Optional<std::chrono::microseconds> request_received_duration_;
  + Optional<std::chrono::microseconds> response_received_duration_;
  };
  } // namespace AccessLog
  