Revert 150990 - [Sync] Avoid unregistering object IDs on shutdown

sync/internal_api/public/sync_manager.h

Index: sync/internal_api/public/sync_manager.h
===================================================================
--- sync/internal_api/public/sync_manager.h	(revision 150991)
+++ sync/internal_api/public/sync_manager.h	(working copy)
@@ -407,19 +407,12 @@
   virtual void UpdateEnabledTypes(
       const ModelTypeSet& enabled_types) = 0;
 
-  // Forwards to the underlying notifier (see comments in sync_notifier.h).
-  virtual void RegisterInvalidationHandler(
-      SyncNotifierObserver* handler) = 0;
-
-  // Forwards to the underlying notifier (see comments in sync_notifier.h).
+  // Forwards to the underlying notifier (see
+  // SyncNotifier::UpdateRegisteredIds()).
   virtual void UpdateRegisteredInvalidationIds(
       SyncNotifierObserver* handler,
       const ObjectIdSet& ids) = 0;
 
-  // Forwards to the underlying notifier (see comments in sync_notifier.h).
-  virtual void UnregisterInvalidationHandler(
-      SyncNotifierObserver* handler) = 0;
-
   // Put the syncer in normal mode ready to perform nudges and polls.
   virtual void StartSyncingNormally(
       const ModelSafeRoutingInfo& routing_info) = 0;