Blogger Carsten Knobloch noticed the new feature earlier today, and TechCrunch also got it working. We tried it on a Google Pixel running the beta version of Android O, but the option didn't show up on our end. A Google spokesperson noted the experimental nature of Canary and said that the ad-blocker was "part of our general approach of running experiments to test possible features that could provide users with the best experience on Chrome."
As such, there's zero guarantee that this ad-blocker shows up in more stable Chrome builds. But given the noise around Google's intention to start blocking more "intrusive" ads, this little test is worth taking note of. Still, it'll probably be a while before it rolls out in a wide fashion -- the WSJ said last month that it likely wouldn't arrive until 2018 to give sites and advertisers time to make sure their ads weren't deemed intrusive.