Adds a snooze button to the sheriff-o-matic ui

The button is configured to snooze the item for 1 hour. The item is deprioritized
in the UI by changing the opacity. Subsequent patches could separate snoozed
items out into a separate collapsible stream.

This patch adds the concept of annotations on a group of failures, 
persisting them in local storage. Subsequent patches should persist
the annotations in a frontend.

NOTRY=true
BUG=399967

Review URL: https://codereview.chromium.org/448503003

git-svn-id: svn://svn.chromium.org/blink/trunk@179897 bbb929c8-8fbe-4397-9dbb-9b2b20218538