[autotest] performance_optional only exists in ToT, do not run it in older branches

This CL can be reverted if CL 257010 is ported back to older branches.

BUG=chromium:465054
TEST=None

Change-Id: I886bc9a18741fb469c867e8626bb86d312dfaa18
Reviewed-on: https://chromium-review.googlesource.com/257211
Reviewed-by: Dan Shi <dshi@chromium.org>
Commit-Queue: Dan Shi <dshi@chromium.org>
Trybot-Ready: Dan Shi <dshi@chromium.org>
Tested-by: Dan Shi <dshi@chromium.org>
1 file changed