Convert tracklist-* tests to testharness.js

Cleaning up tracklist-* tests in media/track to use testharness.js instead of
video-test.js. This will enable to upstream these tests to web-platform-tests.

BUG=588956

Review-Url: https://codereview.chromium.org/1952323003
Cr-Commit-Position: refs/heads/master@{#392585}
4 files changed