[chrome extension]getting default font setting

background.js

"use strict";
(function() {
    var families = ["standard", "sansserif", "serif", "fixed", "cursive", "fantasy"]

    var families

    families.forEach(function(val){
        chrome.fontSettings.getFont({
                genericFamily: val
            }, function(details) {
                console.log(details)
            });
    })
})()

manifest.json

{
        "manifest_version": 2,
        "name": "Test Font",
        "description": "fonts.",
        "version": "0.1",
        "permissions": [
                "fontSettings"
        ],
        "background": {
                "scripts":["background.js"]
        },
}