Parse less and scss files

This pull request is for [Simple support for LESS/SCSS](https://trello.com/c/KoK6kPtp/1190-m-simple-support-for-less-scss-in-key-brackets-features).


We should either have a `@typedef` somewhere in this file defining what SelectorInfo is, or we should use full Closure syntax here to describe it more precisely.  Either way, the rest of the comment after `...} info` becomes unneeded then, since it's just saying in vaguer terms what the type annotation already communicates.