finish converting sheriff-o-matic tests to mocha

BUG=400387
R=ojan@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/476763006

git-svn-id: svn://svn.chromium.org/blink/trunk@180607 bbb929c8-8fbe-4397-9dbb-9b2b20218538