It used to be possible to enable CSS variables support via chrome://flags' #enable-experimental-web-platform-features in previous Chrome builds. Support has since gone again. Hoping for a reappearance soon.

CSS Variables in combination with an additional build step[1] is actually quite usable right now.

[1] https://github.com/segmentio/myth

Edit: The introduction of the new notation as mentioned by heycam, explains Chrome's behavior a bit.