[Sync] Avoid unregistering object IDs on shutdown

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 3e3e14c44f89d32ea2b5753f4d6710119f068f1c..6e8ea6e4f998eb39c29e5e30ac49781c32e5b310 100644
--- a/chrome/browser/sync/profile_sync_service.h
+++ b/chrome/browser/sync/profile_sync_service.h
@@ -38,7 +38,7 @@
 #include "sync/internal_api/public/util/experiments.h"
 #include "sync/internal_api/public/util/unrecoverable_error_handler.h"
 #include "sync/js/sync_js_controller.h"
-#include "sync/notifier/sync_notifier_helper.h"
+#include "sync/notifier/sync_notifier_registrar.h"
 
 class Profile;
 class ProfileSyncComponentsFactory;
@@ -552,15 +552,56 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
   // been cleared yet. Virtual for testing purposes.
   virtual bool waiting_for_auth() const;
 
-  // Updates the set of ObjectIds associated with a given |handler|.
-  // Passing an empty ObjectIdSet will unregister |handler|.
-  // There should be at most one handler registered per object id.
+  // Invalidation clients should follow the pattern below:
   //
-  // The handler -> registered ids map is persisted across restarts of
-  // sync.
+  // When starting the client:
+  //
+  //   pss->RegisterInvalidationHandler(client_handler);
+  //
+  // When the set of IDs to register changes for the client during its lifetime
+  // (i.e., between calls to RegisterInvalidationHandler(client_handler) and
+  // UnregisterInvalidationHandler(client_handler):
+  //
+  //   pss->UpdateRegisteredInvalidationIds(client_handler, client_ids);
+  //
+  // When shutting down the client for browser shutdown:
+  //
+  //   pss->UnregisterInvalidationHandler(client_handler);
+  //
+  // Note that there's no call to UpdateRegisteredIds() -- this is because the
+  // invalidation API persists registrations across browser restarts.
+  //
+  // When permanently shutting down the client, e.g. when disabling the related
+  // feature:
+  //
+  //   pss->UpdateRegisteredInvalidationIds(client_handler, ObjectIdSet());
+  //   pss->UnregisterInvalidationHandler(client_handler);
+
+  // NOTE(akalin): Invalidations that come in during browser shutdown may get
+  // dropped.  This won't matter once we have an Acknowledge API, though: see
+  // http://crbug.com/78462 and http://crbug.com/124149.
+
+  // Starts sending notifications to |handler|.  |handler| must not be NULL,
+  // and it must already be registered.
+  //
+  // Handler registrations are persisted across restarts of sync.
+  void RegisterInvalidationHandler(syncer::SyncNotifierObserver* handler);
+
+  // Updates the set of ObjectIds associated with |handler|.  |handler| must
+  // not be NULL, and must already be registered.  An ID must be registered for
+  // at most one handler.
+  //
+  // Registered IDs are persisted across restarts of sync.
   void UpdateRegisteredInvalidationIds(syncer::SyncNotifierObserver* handler,
                                        const syncer::ObjectIdSet& ids);
 
+  // Stops sending notifications to |handler|.  |handler| must not be NULL, and
+  // it must already be registered.  Note that this doesn't unregister the IDs
+  // associated with |handler|.
+  //
+  // Handler registrations are persisted across restarts of sync.
+  void UnregisterInvalidationHandler(syncer::SyncNotifierObserver* handler);
+
   // ProfileKeyedService implementation.
   virtual void Shutdown() OVERRIDE;
 
@@ -835,11 +876,8 @@ class ProfileSyncService : public browser_sync::SyncFrontend,
   // Factory the backend will use to build the SyncManager.
   syncer::SyncManagerFactory sync_manager_factory_;
 
-  // The set of all registered IDs.
-  syncer::ObjectIdSet all_registered_ids_;
-
   // Dispatches invalidations to handlers.
-  syncer::SyncNotifierHelper notifier_helper_;
+  syncer::SyncNotifierRegistrar notifier_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(ProfileSyncService);
 };