Make the update frequency for sheriff-o-matic 30 seconds again.

Now that the server has been fixed, we should be able to update more
frequently without hitting our spending limit.

Also, only do updates on requestAnimationFrame. That way, background
tabs won't do unnecessary updates. This does mean that when you focus
the tab it will update right then, but I think that's OK.

NOTRY=true

Review URL: https://codereview.chromium.org/483523002

git-svn-id: svn://svn.chromium.org/blink/trunk@180622 bbb929c8-8fbe-4397-9dbb-9b2b20218538