TrayNetworkStateObserver, NetworkIcon, and NetworkList in Ash all care about the portal state of a network. This is currently provided by chromeos::NetworkPortalDetector.

For Mash we need to provide this via mojo.

One straightforward solution would be to add a captive portal state to NetworkState and have NetworkPortalDetectorImpl set that, and reflect that state on cros_network_config.mojom. This should also triger an 'active networks changed' event.