For those wondering, sadly, you cannot get sneak attack damage when using Alchemist's Fire (and likely Acid Flasks or any other grenade-like weapon). Despite the fact that it requires an attack roll it does not qualify. As of right now, there is now were that I've found in RAW myself that specifically states this but, I do have this forum post to go off of from Paizo.
And the first person to reply has a quote apparently from some book source (though which book is not referenced), "Splash weapons cannot deal precision-based damage (such as the damage from the rogue's sneak attack class feature)."
So unless I find or someone else finds something later (or of course DM ruling/house ruling says otherwise) you can not get sneak attack damage with grenade-like weapons.