SessionsSyncManager's initialization sets up bogus native ids before they're fixed later when we have native data. It seems a bit wrong that, on every AssociateWindows() (one happens during initialiation, then on every OnLocalTabModified()), if we don't have native data yet, we end up committing all of our sessions state with the bogus ids from merge.

I suppose everything except the first will get de-duped because the directory is checking for equality, but it feels bad. Especailly in unit tests. It'd be nice if we never committed this bad data, but instead could have an interaction with SyncedSessionTracker that doesn't rely on ResetSessionTracking().