Revert "Enable background video track optimization for MSE content."

This reverts commit df848adb8eb6bf9be13ed82e1b2156b8ae93615a for
the M61 branch due to bugs.

BUG=752726
TEST=none
TBR=tguilbert

Change-Id: I200d16cdbbe982b2723f066414cfb5f64159fd77
Reviewed-on: https://chromium-review.googlesource.com/624663
Reviewed-by: Dale Curtis <dalecurtis@chromium.org>
Cr-Commit-Position: refs/branch-heads/3163@{#712}
Cr-Branched-From: ff259bab28b35d242e10186cd63af7ed404fae0d-refs/heads/master@{#488528}
2 files changed