I think for most people, when they say "available," they mean "without copyright infringement."

As long as you don't distribute chromium with this file, then it will be fine. (You do it yourself).

I'm not sure what the rules are: Google gives me permission to install Chrome, and then, presumably I have permission to delete everything but the PDF viewer plugin, right? Maybe the Chrome EULA disallows this, but, to be honest, I didn't read it.

Ahhh. I couldn't find any information on how to do this the last time I looked.