Keeping this open even if it's fairly similar to bug 822622. Feel free to merge them.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f1baf9ec2968d96b543823fc67d89e9e2d2fbb0b

commit f1baf9ec2968d96b543823fc67d89e9e2d2fbb0b
Author: Tommy Steimel <steimel@chromium.org>
Date: Tue Apr 10 18:00:15 2018

Add hover highlighting for VR on modern media controls

This CL adds hover CSS rules to show a highlight when the media control
buttons are hovered.

Bug:  809021 ,  827568 
Change-Id: I69dfc0d5571efc39226f0e1da30adc211825a402
Reviewed-on: https://chromium-review.googlesource.com/1004119
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Commit-Position: refs/heads/master@{#549585}
[modify] https://crrev.com/f1baf9ec2968d96b543823fc67d89e9e2d2fbb0b/third_party/blink/renderer/modules/media_controls/resources/modernMediaControls.css