function _atob(b64str) {
        if (typeof window !== 'undefined' && window.atob) {
            return window.atob(b64str);
        } else {
            throw new Error('You must supply a polyfill for window.atob in this environment');
        }
    }
Convert a Base64-encoded string into its original representation.
Used for inline sourcemaps.

@param {String} b64str Base-64 encoded string
@returns {String} original representation of the base64-encoded string.