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It looks like maybe bleach or some other chemical has been left to dry on the chrome which caused this.
I use to own a motel and had the chrome rust issue. With the shower chrome rust issue, the thing I found that removed it was a green scourer with a bit of WD-40.
I'm thinking this may work for this as well.
Spray a bit of WD-40 on a green scourer and gently scrub it. - Marty_greenshed
Marty_greenshed has touched on some great ideas there.
The damage looks very similar to aluminium oxidation. Aluminium oxidation will give the appearance of "build up" and will be proud of the surrounding surface.
I'd suggest following Marty's advice and cleaning up the area. Give it a good clean and see if you can scrub it away.
If you are not able to return it to the correct appearance, then you should consider spray painting the trim. You'll need to thoroughly remove any of the WD-40 spray with Sugar Soap, prime the trim, and then spray paint it.
If this is not some chemical residue on the surface that can be removed, it's likely corrosion of the aluminium trim. Once the protective coating is penetrated, the moisture in the air will continue to corrode the surface.
It needs to be scrubbed with a scourer and painted to cease the corrosion. - MitchellMc
