In order to ensure that the user's migration screen is not being bypassed by mistake, we handle the
migration's store COMPLETED state the same way we handle the MIGRATING state.
We can do this because we can treat the initial state (NONE) as being either a fresh start of the
app, either the user's intention of starting the home activity.
Before this change, if the app was being open from the shortcut after the migration was complete,
the user would have been encountered the home activity instead of the migration one.
* With this patch fenix build variants will launch HomeActivity directly from the launcher.
This will get rid of the performance regression outlined in #7818.
* Fennec build variants will launch into MigrationDecisionActivity which will show the
migration UI or launch normally into the app. This is faster than going through
IntentReceiverActivity (measured and perceived).
MarcLeclair