OriginAgentClusterDefaultEnabled

This policy allows origin-keyed agent clustering by default. The Origin-Agent-Cluster HTTP header controls whether a document is isolated in an origin-keyed agent cluster, or in a site-keyed agent cluster. This has security implications since an origin-keyed agent cluster allows isolating documents by origin. The developer-visible consequence of this is that the document.domain accessor can no longer be set. The default behaviour - when no Origin-Agent-Cluster header has been set - changes in M111 from site-keyed to origin-keyed. If this policy is enabled or not set, the browser will follow this new default from that version on. If this policy is disabled this change is reversed and documents without Origin-Agent-Cluster headers will be assigned to site-keyed agent clusters. As a consequence, the document.domain accessor remains settable by default. This matches the legacy behaviour. See https://developer.chrome.com/blog/immutable-document-domain/ for additional details.