Convert video-[default, size, timeupdate]* tests to testharness.js

Cleaning up video-[default, size, timeupdate]* tests
in media/ to use testharness.js instead of video-test.js.
This will enable to upstream these tests to web-platform-tests.

BUG=588956, 310481

Review-Url: https://codereview.chromium.org/2126753002
Cr-Commit-Position: refs/heads/master@{#404214}
6 files changed