Control SafeSites adult content filtering.

Setting the policy controls the SafeSites URL filter, which uses the Google Safe Search API to classify URLs as pornographic or not. When this policy is set to: * Do not filter sites for adult content, or not set, sites aren't filtered * Filter sites for adult content, pornographic sites are filtered The policy applies to both the URL the user navigates to and to iframes. The URLAllowlist policy takes precedence over this policy and can be used to override verdicts from the Google Safe Search API.