SheriffOMatic: Hide failures when a step has too many.

And add a button that lets you see all of them.

BUG=408255
NOTRY=true

Review URL: https://codereview.chromium.org/639523003

git-svn-id: svn://svn.chromium.org/blink/trunk@184130 bbb929c8-8fbe-4397-9dbb-9b2b20218538