Make media/W3C tests be normal js-tests.

Right now they do a bunch of extraneous things, print their
own TEST COMPLETE line  and don't set jsTestIsAsync for
async tests, which makes them flaky.

BUG=316429, 306249

Review URL: https://codereview.chromium.org/68183005

git-svn-id: svn://svn.chromium.org/blink/trunk@161833 bbb929c8-8fbe-4397-9dbb-9b2b20218538