I did this yesterday, what a massive difference using a gamepad is for my platformer...using the 360 wired controller in chrome. It gave me a whole new feeling that it's a real game, the keyboard feels soul-less ;p Plus now I can pretend its on an Ouya...
Initially, I went to the test site Scirra set up,it didn't work. I found a google html5 page with a running game (hurdles). That worked! So I knew chrome was fine. I set it up using the tutorial on this page:
Google Hurdles game