Update testharness.js to latest

Update all copies of testharness.js, testharness.css and idlharness.js,
update expectations where needed, and address a couple of FIXMEs.

Default timeouts are extended per r170136.

R=dpranke@chromium.org
BUG=303251

Review URL: https://codereview.chromium.org/263983002

git-svn-id: svn://svn.chromium.org/blink/trunk@173952 bbb929c8-8fbe-4397-9dbb-9b2b20218538