Switch WebMediaPlayerMS to operate over MediaStreamComponent

... instead of WebMediaStreamTrack.

This is part of the effort to reduce the needless use of
public Blink APIs (wrappers) within renderer/modules.

CL also moves WebMediaPlayerMS away from using WebMediaStream
directly, in favor of MediaStreamDescriptor.

BUG=704136
R=guidou@chromium.org

Change-Id: Ica4bbbf47b5754e2bdd92369e56b7143ebff4727
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2254584


Commit-Queue: Antonio Gomes <tonikitoo@igalia.com>
Auto-Submit: Antonio Gomes <tonikitoo@igalia.com>
Reviewed-by: Guido Urdaneta <guidou@chromium.org>
Cr-Commit-Position: refs/heads/master@{#780829}