We can't change the arguments that we pass to external callbacks. These callbacks are defined by end-users that are using webfont.js (or derivatives like Typekit's kit JS). We should split this back out at this point into two strings. One reason is that we don't want (and can't expect) all users of this JS to change their callback formats. Another reason is that, at that point, we'd have to have all of the `Font` class methods externalized (or at least the public ones) since it'd be interacting with uncompiled code.