This is reproducible on Android on 67.0.3990.1 but not on desktop.

It's probably this commit:

https://chromium.googlesource.com/chromium/src/+/c6de615e45d99287b6ca36f3ed8fe2bf0442726e

Interestingly we are setting the image correctly but it is ignored on Android (it also can be replicated using the mobile simulator in devtools).

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/5632d9ab33eacb3baedb033f2d24230d10288198

commit 5632d9ab33eacb3baedb033f2d24230d10288198
Author: Becca Hughes <beccahughes@chromium.org>
Date: Wed Apr 11 00:58:20 2018

Media Controls: Fix scrim not showing up

Since we moved to the image based scrim it looks like image set
does not properly provide an image at a high pixel ratio.

This provides a quick patch to use media queries instead to
provide the high DPI image. A follow up to this CL will be to
fix the image set property properly.

BUG= 830583 

Change-Id: I77f3ab695facb23f96dcde9e28c57237034f23d1
Reviewed-on: https://chromium-review.googlesource.com/1003274
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549705}
[modify] https://crrev.com/5632d9ab33eacb3baedb033f2d24230d10288198/third_party/blink/renderer/modules/media_controls/resources/modernMediaControls.css

I don't believe this is a CSS parsing bug, though feel free to re-add the component if I missed something.

beccahughes@, should this be closed?