Deprecate and remove Media.MediaElement.PlaybackPositionIsInfinity

It was used to try and root-cause another issue. At this point, the
histogram has expired and enough data has been collected.

Bug: 911298, b/67327907
Change-Id: I92cff00449516672a55efc39720c124e30982937
Reviewed-on: https://chromium-review.googlesource.com/c/1400667
Commit-Queue: Oskar Sundbom <ossu@chromium.org>
Reviewed-by: Mounir Lamouri <mlamouri@chromium.org>
Reviewed-by: Alexei Svitkine <asvitkine@chromium.org>
Cr-Commit-Position: refs/heads/master@{#621980}
2 files changed