Google Chrome Client Certificate Popup
This is what you're looking for:http://www.chromium.org/administrators/policy-list-3#AutoSelectCertificateForUrls
I could tell you how to do it exactly, but my honest opinion is that this is something you have to work out yourself. You need to know what is going on because you are more than likely to run into bugs (not bugs per-se but some undesired or unwanted results).
I have to admit that Google Chrome and Chromium are great browsers, but when it comes to client certificates, they have a lot of improvements to be made.