Ref T10843. There are actually two separate notions of cacheability here:
- Is this cacheable by the browser (e.g., should we emit "Expires: long in the future")?
- Is this cacheable locally (e.g., should we stick it in APC, or just read it off disk every time)?
These got a little mixed up by D15775, so we aren't currently emitting proper "Expires" headers on font files and a few other resource types.
Straighten this out so that we "Expires" these unusual resources correctly.