Backed out changeset 2b3efd1687ec for landing with the wrong bug number.
Bug 978163 - Part 4: Add test for VTTCue::Region. r=rillian

Updated test_texttrackregion.html to reflect the changes as well.

See spec bug: https://www.w3.org/Bugs/Public/show_bug.cgi?id=24380

DONTBUILD