I'm using a lot of PDF files, and they don't generate a good preview/thumbnail.

https://secure.phabricator.com/diffusion/symbol/applyCropAndScale/ has hard-coded attempts to use imagemagic, and then imagecopyresampled, etc.

I want to modulerize this to allow adding implementation - something for PDF (Probably not for upstream), and maybe something that gives a file-type-icon.