How does massive damage death rule interact with wildshaped Druids?

@DangerMcDHow does 5E massive damage death rule interact with wildshaped Druids? Does damage have to pass wildshape HP max or Druid HP max it would have to pass Druid max, IIRC. Apply damage, trigger transformation at 0 to Druid, continue to apply damage

— Mike Mearls (@mikemearls) January 11, 2016