I'm not a chrome user, so I can't comment and I know chrome are releasing updates like there is no tomorrow but v15.x must be at the bleeding edge. So that is a possibility, but the "Scan traffic from well known browser processes only" should in theory work, but If chrome v15.x is using the same chrome executable names it wouldn't exclude chrome.
That said it isn't the chrome executable that is getting blocked, but a file from the game (sorry not a gamer either). Something else a workaround that you could try, presumably the game site IP address is the same each time you could exclude it. From the avastUI, Settings, Troubleshooting, Redirect Settings, WEB, Ignored addresses: and enter the IP address.
This obviously would mean that the web shield wouldn't be monitoring that site (so no web shield protection for that IP, but the web shield would be enabled for the rest of your browsing.