It looks like a Velodyne HDL-32 [1] LiDAR unit. Broadly speaking, it pulses a bunch of lasers (32 in this case) really fast and measures the response time of each beam; think hyper-focused radar. The resulting point cloud can be used to build a high res map of its surroundings essentially in realtime.
Looks similar to what's on top of Google's self-driving cars. I didn't really imagine that much integration between Boston Dynamics and the rest of Google, but perhaps this is a sign that the two groups have joined (or are at least working together).
I don't think the use of LiDAR indicates any connection to the car group. You can pick up a Neato robot vacuum at Wal-Mart for $100 with a spinning LiDAR on top, and that's been on store shelves since before Google acquired their first self-driving car team. It's just the go-to sensor for mapping your surroundings in near-realtime.
I wonder why it's obscured so much by what looks like protective housing in some shots. I also wonder how much of its navigation it's actually doing, as opposed to being remote controlled.
