A320 First Officer reporter the inner pane of the Captain's side window cracked during approach. Flight crew continued approach to a safe landing.

Narrative

While on radar vectors base turn to final for runway XXL at ZZZ; descending through approximately 4;000 feet MSL 23°C on the ground; VMC; all other conditions normal; I heard a small pop then the Captain said 'wow my window just cracked.' At first we thought it was the outer pane of his escape window. He had the yellow sunshield extended; we could both see spider webbing glass. We were so close to the airfield with no additional traffic in the vicinity that we decided not to say anything to ATC rather than [request assistance]. Our rationale was that the best thing to do was get the plane out of the air as fast as possible and both focus on those procedures rather than inducing additional distraction or delay. On final; the Captain noted that little pieces of glass were falling off. It was then we realized the inner pane had broken. I mentally prepared myself to take the plane in the event the conditioning worsened; and the Captain was unable to continue flying. He made a smooth landing and we landed uneventfully. Once at the gate; we told the CSR who reported it to maintenance; then we contacted Maintenance Control and wrote it up.