Chain of evolution, means ancestors of chicken/egg were neither egg or chicken necessarily rather they were called something different but that happens gradually but to be specific, you have to give the credit to egg, what actually came "first" in this process, because Let's say -

A -> chicken -> egg (if this is the case, then chicken wouldn't be called a chicken in the first place because it didn't come from egg)
A -> egg - > chicken (if this is the case then, both holds true, because chicken came from egg, that's true. An egg is ALWAYS AN EGG, doesn't matter if it came from "typical" chicken or from something alike chicken or chicken ancestors)