[sync] Isolate FOREIGN_SESSION_UPDATED notification in ProfileSyncService

chrome/browser/sync/profile_sync_service.h

Index: chrome/browser/sync/profile_sync_service.h
diff --git a/chrome/browser/sync/profile_sync_service.h b/chrome/browser/sync/profile_sync_service.h
index 3309efd6e87fcb9a315c1d681d28619c49b09802..c82f4c05c4695d98a9386ae9ac332bdc7470340f 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -39,6 +39,8 @@
 #include "components/sync_driver/sync_prefs.h"
 #include "components/sync_driver/sync_service.h"
 #include "components/sync_driver/sync_stopped_reporter.h"
+#include "content/public/browser/notification_observer.h"
+#include "content/public/browser/notification_registrar.h"
 #include "google_apis/gaia/google_service_auth_error.h"
 #include "google_apis/gaia/oauth2_token_service.h"
 #include "net/base/backoff_entry.h"
@@ -178,6 +180,7 @@ class ProfileSyncService : public sync_driver::SyncService,
                            public sync_driver::DataTypeManagerObserver,
                            public syncer::UnrecoverableErrorHandler,
                            public KeyedService,
+                           public content::NotificationObserver,
                            public OAuth2TokenService::Consumer,
                            public OAuth2TokenService::Observer,
                            public SigninManagerBase::Observer {
@@ -641,6 +644,11 @@ class ProfileSyncService : public sync_driver::SyncService,
   friend class TestProfileSyncService;
   FRIEND_TEST_ALL_PREFIXES(ProfileSyncServiceTest, InitialState);
 
+  // Observe notifications.
+  void Observe(int type,
+               const content::NotificationSource& source,
+               const content::NotificationDetails& details) override;
+
   // Stops the sync engine. Does NOT set IsSyncRequested to false. Use
   // RequestStop for that. |data_fate| controls whether the local sync data is
   // deleted or kept when the engine shuts down.
@@ -981,6 +989,8 @@ class ProfileSyncService : public sync_driver::SyncService,
   // IsPassphrasePrompted sync preference.
   bool passphrase_prompt_triggered_by_version_;
 
+  content::NotificationRegistrar registrar_;
+
   base::WeakPtrFactory<ProfileSyncService> weak_factory_;
 
   // We don't use |weak_factory_| for the StartupController because the weak