Seems not a regression. I retryed 9587.0.0 and it failed.

fail message:
"Video failed to load. Player expected status: Playing and current status: Unstarted."

Probably something in YouTube changed. Avinash, could you take a look?

This is related youtube video, as it is not longer available. Need to change the video URL.

Quick update, since this is a frequently occurring scenario, Avinash decided that it would be a good idea to create our own test video and upload it to Youtube so that we don't fail due to other publishers' activities. 

This test turned green from R60-9592.0.0 as youtube video available.. :)

Avinash@, do you mean that video is back online? Either way, we should upload our own. 

yes, it is back online. Anyway I'll upload our own video in some test account for testing.

May I ask for an update please? Thank you.

we've uploaded video into our testing acc and started using for regular testing. Will update into automation test. 
Video URL: https://www.youtube.com/watch?v=55HFORAkYdo

The following revision refers to this bug:
  https://chromium.googlesource.com/chromiumos/third_party/autotest/+/1cf97435c6272d8821017ffef4f8b67caf343040

commit 1cf97435c6272d8821017ffef4f8b67caf343040
Author: avinash kodipelli <avkodipelli@chromium.org>
Date: Wed Jun 21 02:30:19 2017

Using testing account youtube video for test

Changing youtbe video to test account video for avoiding any
permission issues and unavailability of video.

BUG= chromium:726575 
TEST=manual

Change-Id: Ic6286eba5d5fd613ef051bf6287c606d3a5ebcac
Reviewed-on: https://chromium-review.googlesource.com/541855
Commit-Ready: Avinash Kodipelli <avkodipelli@chromium.org>
Tested-by: Avinash Kodipelli <avkodipelli@chromium.org>
Reviewed-by: Vinayak Suley <vsuley@chromium.org>

[modify] https://crrev.com/1cf97435c6272d8821017ffef4f8b67caf343040/client/site_tests/video_YouTubeHTML5/youtube5.html

Closing as per https://cros-goldeneye.corp.google.com/chromeos/healthmonitoring/testDetails?testName=video_YouTubeHTML5&suite=&daysBack=1&board=&architecture=&boardFamily=&buildConfig=&reason=&version=&milestone=61&dut=