Here's the error:

../../chrome/browser/picture_in_picture/picture_in_picture_window_controller_browsertest.cc(529): error: Value of: window_controller()->GetWindowForTesting()->GetVideoLayer()->visible()
  Actual: false
  Expected: true

https://chromium.googlesource.com/chromium/src/+/93488940ae5770af18ca5405395a206b426756a6/chrome/browser/picture_in_picture/picture_in_picture_window_controller_browsertest.cc#529

Any idea how to fix this test?

Would it help to check if the video is actually playing before ack the src change?

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/42ec5b3d10370d86089c296c3486c2c5eb3be572

commit 42ec5b3d10370d86089c296c3486c2c5eb3be572
Author: François Beaufort <beaufort.francois@gmail.com>
Date: Wed Jul 25 19:57:40 2018

Fix Picture-in-Picture test flakyness.

Bug:  865821 
Change-Id: I0b288faa7e17889665560d59d46e41f7072102b7
Reviewed-on: https://chromium-review.googlesource.com/1150174
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Commit-Queue: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#578026}
[modify] https://crrev.com/42ec5b3d10370d86089c296c3486c2c5eb3be572/chrome/browser/picture_in_picture/picture_in_picture_window_controller_browsertest.cc
[modify] https://crrev.com/42ec5b3d10370d86089c296c3486c2c5eb3be572/chrome/test/data/media/picture-in-picture/window-size.html