Add const, virtual and override keywords.
(I)TRT_DriftFunctionTool
http://atlas-computing.web.cern.ch/atlas-computing/links/distDirectory/gitwww/experimentalWebArea/nicos_web_areaconstmaster_Athena_x86_64centos7gcc8opt64BC7G8AthenaOpt/NICOS_Log_2019-06-08T1008/InnerDetector_InDetRecTools_TRT_DriftCircleOnTrackTool.html