init.json does not always exist if we use `variant.js` for homescreen customization tool on [bug 897325](https://bugzilla.mozilla.org/show_bug.cgi?id=897325) (because we didn't execute applications-data.js first for customization tool), I suggest extracting homescreen customization code in applications-data.js into a function and export it, than you can use it to get customized grid layout for validation.

e.g., https://gist.github.com/yurenju/7348543#file-applications-data-js-L153-L166

feel free to find a better way to handle this situation.