My guess is that a mild refusal would be acceptable to Google. They are unlikely to be put off by a change of subject.

A hard refusal might annoy them, if they persist in asking.

I suggest naming a very high figure first, to gain benefit from the anchoring effect. Then mentioning your salary will make it the anchor for the negotiation. Google has a reputation for paying high salaries.

If you are looking for advice on negotiation, I suggest searching for 'anchoring' as well as 'negotiation, to get more evidence-based advice.

Good luck.