Chrome Version       : 67.0.3369.0
Operating System     : Android 8.1.0; Pixel 2

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

What is the expected result?
The amount of time skipped should be the one defined in "seekbackward" and "seekforward" as Media Session has set two action handlers for those.

What happens instead of that?
It uses arbitrarily 10 seconds.

I think website has a better vision of the amount of time and it should use the one defined in Media Session. Moreover, this time could be based on a user preference.