Show how long a test has been failing in sheriff-o-matic.

BUG=405241
R=cbiesinger@chromium.org

Review URL: https://codereview.chromium.org/478423003

git-svn-id: svn://svn.chromium.org/blink/trunk@180754 bbb929c8-8fbe-4397-9dbb-9b2b20218538