It would reduce it. The only way a P38 would have a chrome lined barrel would be as a result of aftermarket work, or by swapping in a postwar P1 barrel, which would reduce its value for having mismatched parts.
The P38 was manufactured during wartime, when simpler, less expensive ways of manufacturing things were sought out. Chrome lining - especially on a pistol barrel - would've been highly unlikely on a P38. If you have such a pistol, what you probably have is a postwar P1 pistol (aluminum slide, rather than steel), or else a P38 with a postwar P1 barrel swapped in.
10-100 USD or so
You will need a professional appraisal.
Which pistol? Most production pistols have a barrel length of 1 to 8 inches.
From mouth of barrel to where it meets the cylinder.
yes
A pistol is a single hand firearm with a short barrel.
No
125mm
Serial numbers do not mean a lot- we need make and model. Also- not all revolvers with "38 S&W" on the barrel ARE Smith & Wessons- that is a caliber. And the finish is nickel, not chrome.
100 USD
One can make a pistol much larger than it needs to be, maybe even having an extra-long barrel would make a pistol larger, technically. I'll assume you mean the barrel diameter. Although it would seem that a .380 and .38 would have the same barrel diameter, namely, 38/100th of an inch, that is not usually very accurate. The .380 ACP has an actual barrel diameter of about .35 caliber, or 35/100th of an inch. The .38 Special has a barrel diameter of .357 caliber, or 35.7/100th of an inch. So the .38 Special has an ever so slightly larger diameter.