Chrome Version       : 67.0.3369.0
OS Version: 10489.0.0

What steps will reproduce the problem?
1. Go to https://googlechrome.github.io/samples/media-session/video.html
2. Enable "New Media Controls" flag at chrome://flags/#enable-modern-media-controls
3. Click "Play" button

What is the expected result?
Since Media Session has set 'previoustrack' and 'nexttrack' Action Handlers, it would be great to show new previous and next track buttons to the new media controls.
Note that these buttons are already shown in Media Session notification buttons on Android. See https://developers.google.com/web/updates/2017/02/media-session 

What happens instead of that?
For now, there's nothing.

See mock for what it could look like.
 

Deleted: current.png 1.1 MB

	current.png 1.1 MB View Download

Deleted: mock.png 1.5 MB

	mock.png 1.5 MB View Download