I couldnt find where it calls BeginDraw or EndDraw either so I just set it in the draw method
EndDraw doesnt do anything but it slows to a crawl after about 2-3 secopnds without clearing the drawnode in BeginDraw.
If anyone else is having trouble adapting to chipmunk in v3 here is a template I have set up. Its Cocos2d 3.2 with Box2D 2.3.1 with the above GLESDebugDraw.
I dont know of any problems but if you find one let me know. Adding Box2D to an existing project isnt very fun