Convert track-language* and track-large* tests to testharness.js

Cleaning up track-language* and track-large* 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/1938533002
Cr-Commit-Position: refs/heads/master@{#391588}
6 files changed