Move tree closers to the top in sheriff-o-matic.

Tree closers should be prominent and not show up in the failedOnce list.
Even if they fail once, the sheriff needs to pay attention to it ASAP.

NOTRY=true
BUG=400397
R=leviw@chromium.org

Review URL: https://codereview.chromium.org/629743002

git-svn-id: svn://svn.chromium.org/blink/trunk@183430 bbb929c8-8fbe-4397-9dbb-9b2b20218538