I was just diagnosing some memory issues and found that the nacl_helper in google chrome was chewing up 84.0G.  Some searching on this floated a hit from May 2016 that identified the Google Play Music extension as a potential source.  I use Google Play Music so disabled the extension.  The nacl_helper process was killed off immediately.  Google Play Music still runs in the browser without the extension so I'm going to just leave that disabled and see if I notice any difference at all. Hopefully not.