message: Fix warning in clang 6.0.0
diff: @@ -37,7 +37,7 @@ public:
  MetricTimerResult();
  ~MetricTimerResult();
  double get_elapsed_seconds() const;
  - virtual void report_seconds(double time);
  + void report_seconds(double time);
  protected:
  double m_elapsed_seconds;
  };
  