[sync] Isolate FOREIGN_SESSION_UPDATED notification in ProfileSyncService

components/sync_driver/sync_service_observer.h

Index: components/sync_driver/sync_service_observer.h
diff --git a/components/sync_driver/sync_service_observer.h b/components/sync_driver/sync_service_observer.h
index f0e6d913efff0fac3bdf737ad507674fc6f767da..d168f41709bc06da137182efd679295c2ac3ac25 100644
--- a/components/sync_driver/sync_service_observer.h
+++ b/components/sync_driver/sync_service_observer.h
@@ -30,6 +30,9 @@ class SyncServiceObserver {
   // process.
   virtual void OnSyncConfigurationCompleted() {}
 
+  // Called when a foreign session has been updated.
+  virtual void OnForeignSessionUpdated() {}
+
  protected:
   virtual ~SyncServiceObserver() {}
 };