Nickle plating has been around since (at least) the middle of the 19th century as a gun finish and is very decorative. It is a bit fragile, and can age, turn yellowish, chip, and peel over time. Very few guns are now available (new) with a nickle finish.
Chrome plating can be purely decorative, too. When a car shop chrome plates a bumper, that's not the kind of surface you want on a gun.
"Hard chrome" or industrial chrome plating is a completely different process, providing an extremely durable surface similar to what's installed on mechanical components like hydraulic pistons and such that have to remain smooth and corrosion-free under very demanding conditions. It is a terrific treatment, but has only become somewhat commonly available for guns in the last 10-15 years.