[Global Media Controls] Don't update active media session on tab focus

This CL removes the MediaSessionImpl logic that requests audio focus
when the WebContents is focused. This logic was there to ensure that a
focused tab playing audio would have the active Media Session, but we
have decided to not have that functionality.

Bug: 923208
Change-Id: Idb5977d425e51f01b9c291d52f3183e2983ae220
Reviewed-on: https://chromium-review.googlesource.com/c/1437534
Commit-Queue: Tommy Steimel <steimel@chromium.org>
Reviewed-by: Becca Hughes <beccahughes@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#627094}(cherry picked from commit 03bc24e5096e4a27487f4a318627ea068979e6be)
Reviewed-on: https://chromium-review.googlesource.com/c/1450303
Reviewed-by: Tommy Steimel <steimel@chromium.org>
Cr-Commit-Position: refs/branch-heads/3683@{#123}
Cr-Branched-From: e51029943e0a38dd794b73caaf6373d5496ae783-refs/heads/master@{#625896}
3 files changed