Update video-playing-and-pause.html test to use async_test(function(test) style.

BUG=248265

Review URL: https://codereview.chromium.org/155853003

git-svn-id: svn://svn.chromium.org/blink/trunk@166750 bbb929c8-8fbe-4397-9dbb-9b2b20218538