The slang term is far from being outdated, because it is still in use. Perhaps you have never heard it yourself, but I have.
I first encountered it through a hacker friend of mine in the early 90s in - of all places - Lincoln, Nebraska. He had spent some time out of the state working for the now-defunct maker of Sharebase. He returned to Nebraska after the demise of that company, and told me about the hacker culture and lexicon years before I graduated with my Comp Sci degree in 1993. I didn't know what to make of it at the time, but once the internet hit its inflection point I got online and found the Jargon File, of course.
I remember him using the word "chrome" to describe the GUI user-interface parts of a program (with a somewhat dismissive tone, because he considered to be uninteresting). This was in contrast to the non-chrome parts of programs, which he found more engaging. I have since witnessed it used in this way by several others.
In fact, I worked with a team of programmers on an internal system at a large market research firm who named major releases of a home-grown web templating system - because we thought dotted numbers were boring - after words out of the jargon file. We went through five major releases before this practice was retired: amiga, blob, chrome, dogcow, and eliza.
(Incidentally, one of my colleagues from that team went on to become a Program Manager for Google's browser project...although the browser already had the name before he joined.)
Now here's the kicker: think about what the word "chrome" signifies in Mozilla. It's a URL resource-type designator for referring to XUL markup, right? Well, what is XUL for? It's a markup language for the user-interface aspects of the mozilla browser...the browser's chrome. The hackers behind the mozilla project likely used this word because it was already in somewhat-common usage...and probably to amuse themselves. Perhaps this historical fact is inadequately documented, but to those of us who encountered this part of the lexicon in active use the truth is as plain as day.
Now consider Google's browser. Did they re-invent the rendering engine? No. The bulk of that browser's plumbing - with the notable exception of Lars Bak's javascript runtime and the multiprocess model - was something that they grabbed off the shelf, leaving the main contribution that differentiates the browser is the user-interface aspects of the program...the chrome. While Apple had already brought WebKit to the Windows world, they had utterly failed to make a UI that had any appeal to Windows users. Google created a browser whose chrome was more at-home, as it were. I would not be surprised if this was the genesis of the name.
I've heard people complain that they stole the word 'chrome' from mozilla before. I find that to be an absurd notion, however, given the word's history in hacker slang.