[Sync] Avoid unregistering object IDs on shutdown

chrome/browser/sync/glue/sync_backend_host.h

Index: chrome/browser/sync/glue/sync_backend_host.h
diff --git a/chrome/browser/sync/glue/sync_backend_host.h b/chrome/browser/sync/glue/sync_backend_host.h
index bafe1402f07628a69c6ba5e6ba88ab556163d912..65622b286081ca2689d8c6542ed207bed9700cba 100644
--- a/chrome/browser/sync/glue/sync_backend_host.h
+++ b/chrome/browser/sync/glue/sync_backend_host.h
@@ -180,7 +180,8 @@ class SyncBackendHost : public BackendDataTypeConfigurer {
   void UpdateCredentials(const syncer::SyncCredentials& credentials);
 
   // Registers the underlying frontend for the given IDs to the
-  // underlying notifier.
+  // underlying notifier.  This lasts until StopSyncingForShutdown()
+  // is called.
   void UpdateRegisteredInvalidationIds(const syncer::ObjectIdSet& ids);
 
   // This starts the SyncerThread running a Syncer object to communicate with
@@ -211,9 +212,11 @@ class SyncBackendHost : public BackendDataTypeConfigurer {
   bool SetDecryptionPassphrase(const std::string& passphrase)
       WARN_UNUSED_RESULT;
 
-  // Called on |frontend_loop_| to kick off shutdown procedure. After this,
-  // no further sync activity will occur with the sync server and no further
-  // change applications will occur from changes already downloaded.
+  // Called on |frontend_loop_| to kick off shutdown procedure. After
+  // this, no further sync activity will occur with the sync server
+  // and no further change applications will occur from changes
+  // already downloaded.  Furthermore, no notifications are sent to
+  // any invalidation handler.
   virtual void StopSyncingForShutdown();
 
   // Called on |frontend_loop_| to kick off shutdown.
@@ -530,6 +533,10 @@ class SyncBackendHost : public BackendDataTypeConfigurer {
   // UI-thread cache of the last SyncSessionSnapshot received from syncapi.
   syncer::sessions::SyncSessionSnapshot last_snapshot_;
 
+  // Whether or not we propagate notifications to invalidation
+  // handlers.
+  bool propagate_invalidations_;
+
   DISALLOW_COPY_AND_ASSIGN(SyncBackendHost);
 };