Extension:Collection lets you make custom collections for rendering, as well as rendering "saved books" or "just one article".
Both of the latter have corresponding URLs that I would like to log, so that we can easily see the source of a buggy request or DoS.
Because of the way the extension is written, we've lost the source information by the time we invoke OCG. We should preserve the 'source URL' in the extension, where such a thing makes sense, and then pass it to OCG so that it can use it in its logs.