I suspect that "extracting" this part of chrome into a library would result in the same thing: a library that starts up the full chrome environment and prints a

I suspect that "extracting" this part of chrome into a library would result in the same thing: a library that starts up the full chrome environment and prints a page to PDF. The PDF-ization isn't the part that's hard to extract (there are libraries to create PDFs from scratch already available, and they're small/intelligible). Rather, it's the rendering of a webpage for display that's the hard part, and what most of the code in any web browser is concerned with. Whether that display is a monitor or a PDF doesn't change much.