Method print_used_time

lite/example/cpp_example/helper.h:74–80

        return static_cast<double>(u.count()) / 1000000.0;
    }
    void print_used_time(int iter) {
        m_stop = Clock::now();
        std::chrono::duration<double> elapsed = m_stop - m_start;
        Nsec u = std::chrono::duration_cast<Nsec>(elapsed);
        printf("%s used time %f ms\n", (m_name + std::to_string(iter)).c_str(),
               static_cast<double>(u.count()) / 1000000.0);
    }
    void reset_start() { m_start = Clock::now(); }

private: