I recently came across something like that for opensource Java code, called `grepcode`:

http://grepcode.com/file/repository.grepcode.com/java/root/j...

It supports quite a big number of Java code repositories it seems.

Edit: Also sourcegraph (linked in a link in a sibling post) does something similar:

https://sourcegraph.com/github.com/gorilla/websocket/-/blob/...