Chrome (and chromium) calls the feature "field trials" and there doesn't really seem to be a way to opt out. I'm seriously baffled by the audacity of Google here.
Seems as if the only way to actually get rid of them is to modify the Chromium codebase and compile it yourself.
It might be worth to investigate whether there is some kind of host name that could be nullified on the network, of the server that the trials are loaded from.
Sorry for that misinformation, I clearly have to update my original rant.