A light meter inside a DSLR is very much the same as a stand-alone light meter. In both cases it is basically a photo-electric sensor that displays in one way or the other the intensity of the electrical current that the given amount of light generates. The manner in which that data is displayed is simply a matter of user interface. A histogram is, in a nutshell, a distribution curve of the signal strength across any given matrix of individual photocells that comprise the sensor. Any modern spotmeter could feature the same thing if equipped with an appropriate display and software/firmware, but all it would really accomplish would be to raise the price. DSLRs have it simply because they already have both the software and the display.
The question is not whether an electronic sensor could be calibrated to a film, the question is which film it should be calibrated to? And, at least in case of B&W films, which developer as well...
Just like with stand alone light meters, it is ultimately up to the photographer to interpret the data provided by a measuring device and translate that into desired tones and DR. With that in mind, which measuring device one uses is pretty much a matter of personal preference.
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