js2-mode is no longer developed and we recommend js-mode these days,
so switch the modelines to specify that, and make them consistent
across all files.
https://bugzilla.gnome.org/show_bug.cgi?id=660358
The original support for CSS based shadows has been extended with
support for an optional spread radius and the 'inset' keyword,
so with the additional complexity a dedicated test case looks
appropriate.
https://bugzilla.gnome.org/show_bug.cgi?id=642334