[TTWF Shanghai]Tests for css3 box shadow from Mark

Reviewed by @ArchangelSDY at TestTWF Shanghai, still need work:

1. It seems to be more like a test for outline than box-shadow.
2. I'm not sure if any spec has defined the right behavior for an UA in this situation. Here's a related bug for
Firefox: https://bugzilla.mozilla.org/show_bug.cgi?id=480888.