function toJson(theme) {
    var jsonTheme = {};
    for (var _i = 0, _a = Object.keys(jsonTheme); _i < _a.length; _i++) {
        var key = _a[_i];
        var style = jsonTheme[key];
        jsonTheme[key] = style._styles;
    }
    return jsonTheme;
}
Converts a [[Theme]] with formatter functions to a [[JsonTheme]] with string values. Used by [[stringify]].