Make marking a reftests as NeedsRebaseline/NeedsManualRebaseline a lint error.

There's no way to rebaseline reftests. So, error on the linter instead of
after people have committed the patch and the auto-rebaseline runs.

Review URL: https://codereview.chromium.org/134663004

git-svn-id: svn://svn.chromium.org/blink/trunk@165013 bbb929c8-8fbe-4397-9dbb-9b2b20218538