Introduces a new violation type called "Potential Permissions Policy violation", which will only look at Permissions Policy (including report-only policy) and the allow attribute set in iframes to detect the conflict between Permissions Policy enforced vs permissions propagated to iframes.
Permissions Policy violation reports for cross-origin iframes are only sent to the iframe's reporting endpoint and not to the embedder's reporting endpoint, because of the concern that it might leak sensitive information about a cross-origin iframe. However, this makes it difficult for sites to enforce Permissions Policy because it can't learn about breakages in cross-origin iframes. This feature introduces a new violation type called "Potential Permissions Policy violation", which will only look at existing Permissions Policy (including report-only policy) and the allow attribute set in iframes to detect the conflict between Permissions Policy enforced vs permissions being propagated to iframes. Since both Permissions Policy and allow attributes are set by the embedder, this feature does not leak any new information to the embedder. However, potential Permissions Policy violations will be sent when an iframe is loaded, and not when the iframe uses the prohibited feature, which is different from the normal Permissions Policy violations (hence the name "potential").