Add layout test to verify timeupdate event doesn't fire before playing.

It requires some Chromium changes before it'll start passing.

BUG=223476

Review URL: https://codereview.chromium.org/343263002

git-svn-id: svn://svn.chromium.org/blink/trunk@176687 bbb929c8-8fbe-4397-9dbb-9b2b20218538