a simple chrome coating can add a few seconds of protection for a shell, enough to prevent it from being destroyed before it reaches its target.
Any chrome or metal coating added to a missile or shell that is designed to increase reflectivity, will (very likely) increase the radar reflectivity of the object. That may have the unintended consequence of making the object more susceptible to standard intercept missiles which use radar guidance. It will be difficult to defend against both defensive possibilities, giving flexibility on the tactical side in which method (laser, radar guidance) is most effective.
Happiness is twin floppies.