Temporarily lower the update frequency for sheriff-o-matic.

30s-->300s. This is to avoid hammering the backend while we fix the
load issues.

BUG=401358
TBR=eseidel@chromium.org,szager@chromium.org

Review URL: https://codereview.chromium.org/445133004

git-svn-id: svn://svn.chromium.org/blink/trunk@179683 bbb929c8-8fbe-4397-9dbb-9b2b20218538