NetworkMetricsProvider, which lives in the browser process, currently calls NetworkChangeNotifier::FinalizingMetricsLogRecord (1), which we want to only live in the network process. FinalizingMetricsLogRecord only does anything on Android (2), where it sets the NCN.CellularConnectionSubtype histogram. We should figure out how/if to migrate this.

1: https://cs.chromium.org/chromium/src/components/metrics/net/network_metrics_provider.cc?l=185
2: https://cs.chromium.org/chromium/src/net/android/network_change_notifier_android.cc?l=235