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Fails consistently on my Linux workstation and also seems to have
trouble on a variety of bots that actually have camera hardware,
so disable everywhere.

The primary cause seems to be that this will flake other tests when
run in parallel.

BUG=417824
TEST=all media_unittests pass when a camera is attached.

Review URL: https://codereview.chromium.org/1428853003

Cr-Commit-Position: refs/heads/master@{#357147}