GitLab

This CL moves the MPRIS implementation into the SystemMediaControls
component. It deletes the usage of the MPRIS-specific API in favor of
the platform-agnostic SystemMediaControls API.

Public design doc:
https://docs.google.com/document/d/1_UjhXdXzQlPEwFKpogTZm-ILylKid4lTiOomqHv-IPg/edit?usp=sharing

Bug: 949596
Change-Id: I2af605dd742969fa474dfe14ec62167ebb80852b
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1895385Reviewed-by: Scott Violet <sky@chromium.org>
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/heads/master@{#711904}