I discovered the videos in January. One of the first I saw was posted by the irreverent online car magazine Jalopnik. “Dangerous Idiot Sleeps While Driving His Tesla on Autopilot,” read the headline. The cellphone-captured footage did, as promised, appear to show a man snoozing in the driver’s seat of a Tesla as it zipped along a road somewhere outside Las Vegas. And because the man was asleep, it was safe to assume that navigation was indeed being handled by the car’s onboard driving-assistance system, which is called Autopilot.