[Sync] Sync client should to exponential backoff when receive partial failure

components/sync/engine_impl/sync_manager_impl.cc

Index: components/sync/engine_impl/sync_manager_impl.cc
diff --git a/components/sync/engine_impl/sync_manager_impl.cc b/components/sync/engine_impl/sync_manager_impl.cc
index 06720a0318cd330c99eae2c460fe70087c2c9989..7a3466d019f9677252cc1452e80be7f5d712afa6 100644
--- a/components/sync/engine_impl/sync_manager_impl.cc
+++ b/components/sync/engine_impl/sync_manager_impl.cc
@@ -855,6 +855,8 @@ void SyncManagerImpl::OnRetryTimeChanged(base::Time) {}
 
 void SyncManagerImpl::OnThrottledTypesChanged(ModelTypeSet) {}
 
+void SyncManagerImpl::OnBackedOffTypesChanged(ModelTypeSet) {}
+
 void SyncManagerImpl::OnMigrationRequested(ModelTypeSet types) {
   for (auto& observer : observers_) {
     observer.OnMigrationRequested(types);