Gardening. media/media-controller-playbackrate.html marked as Fail for Mac Release

BUG=414649
TBR= scherkus@chromium.org, philipj@opera.com
NOTRY=true

Review URL: https://codereview.chromium.org/574593004

git-svn-id: svn://svn.chromium.org/blink/trunk@182046 bbb929c8-8fbe-4397-9dbb-9b2b20218538