I have two dogs - One who is an Australian Kelpie, about 8 years old whom I adopted many, many years ago and one 7 year old Chihuahua, who I adopted Feb 2011.
With the first dog, she had a toy that was a stuffed animal that she treated very gently. We referred to it as 'baby' she would not tear it apart like other toys, so we carried this word onto kittens and actually practically mothers them. Our cats have all grown up with her and love on her in that way.
Now, last year I got the chihuahuha, and we knew nothing about how he would react to cats. He honestly just did not care and still does not. He...lays on them and with them, and loves them in the same fashion. Neither of my dogs have ever actually chased my cat when the cat was not /baiting/ the dog into playing.
My chi is far FAR tinier than all my cats. He plays with them just as much as they do with him. However, he does get annoyed when he gets ganged up on. (I have 4 cats, I live on a farm, so I have rabbits, goats, sheep, peacocks, burros..the whole 9 yards.)
But, primarily? I have had success with essentially teaching my dogs that the cats are part of their pack.
My Kelpie, who is about 60 pounds will defend them from other dogs or animals. My cats no longer go outside (I live too far into the wilderness now to safely keep my cats from being coyote or bobcat bait - we've got one roaming through). But when they did, my kelpie would chase off other dogs. To the point where if they did not back off she would fight with them.
Now the Chi does..not really even seem to care, but I think he thinks they are part of his pack. His life is so centric around me that I can't imagine him ever caring enough about anything else. We suspect he was neglected. The only thing he cares about outside of eating and going potty is being with me. I wear a bathrobe in the house so he can hang around with me when we aren't playing with the cats or walking outside. I never go outside at night without both dogs because of the predators.
This is such a large image I am linking it. But here he is laying on my manx cat:
Mo on Bounce
I have much better pictures of my little 4 lbs baby, just not resized and I am about to sleep! But, the point is - Most dogs chase cats because they have never really been properly introduced to them or trained. I have no idea if Mo ever encountered cats previously, but I know at least that my kelpie encountered them at a young age. Your chi is young. If you are considering a cat, I'm guessing you are considering a kitten. I would honestly be more worried about them misinterpreting play, than aggression at this point. The cat if old enough, will likely not feel threatened enough by a chihuahua to do more than smack it if it does something the cat perceives as stupid.
If you can establish some kind of word, or introduction to the cat/or vice versa, that is not risky to either animal. Do so.
When we got new kittens (I rescued 3 feral siblings, and had the manx already), we introduced them to the manx, and the big dog first with care, by picking up the cat and introducing it butt first to the other animals. This lets the other animals know they are not a threat, because they cannot see their faces and the cat or dog is not in an active threatening or defensive posture. It lets you also carefully introduce more than just the smell. Some cats will hiss at first, that's normal.
You just keep re-introducing them slowly until the cat's curiosity gets ahead of feeling threatened. Or the dog's. I'd suggest just making sure you had control in the situation, let them get to know one another and then keep them separated for a few days. Let the cat have roam of the main areas of the house for some hours of the day to get acclimated to where hiding places are, and possibly. Introduce the dog when the cat is somewhere out of reach, on the back of a sofa or a table. Let the dog roam the floor so they can observe one another.
Granted, my dog has raised several different kittens now. The 3 we got 8 months ago? Were her 3rd, 4th, and 5th, respectively. She has encountered adult cats as well. I think it's a pity she never got to be a mother herself, as her breed is not particularly well known and she would have been a great momma.
However, she doesn't chase our peacocks, our cats, or our rabbits at all anymore. Because to her? We have reinforced and have good enough verbal training with her that she knows they are babies and that if she chases, she will get in trouble. (She's really a very sensitive dog, just raising your voice makes her very upset, so she's super well behaved.)
I am not sure how easily 'baby' as a word would transfer over. As we referred to her stuffed lion as 'baby' long before she really ever got trained to use it in relation to cats, kittens, rabbits and birds..but, it's worth a try.