GitLab

Adds position state to WMPI. This is a combination of
playback rate, duration and current time and is used
to display the playback position in the UI.

The next step is sending this to the browser process.

BUG=985394

Change-Id: I76a3671d6357d5fb620e05857e3519de6707fbc3
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1706777Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Reviewed-by: Chrome Cunningham <chcunningham@chromium.org>
Commit-Queue: Becca Hughes <beccahughes@chromium.org>
Cr-Commit-Position: refs/heads/master@{#680458}