I honestly don't know what's the point of mentioning an offer to your current employer. If you have a better offer - take it, don't let me hold your career back, good luck, no hard feelings on my side.

From my experience the reason why employees who have another offer even bother to mention it to their current boss, asking for counter, is because that other offer has some serious downside that prevents them from just accepting it right away.

Anyway, I can probably replace you with someone that will gladly take your current salary. And if I can't and end up paying your replacement the money you demanded (or more) at least I'll be paying that to the guy who is happy to work for me, not to someone who is already actively looking for other jobs.