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

components/sync/engine_impl/all_status.cc

Index: components/sync/engine_impl/all_status.cc
diff --git a/components/sync/engine_impl/all_status.cc b/components/sync/engine_impl/all_status.cc
index 5552eefbb4d9d8285a15bf1f03fcbf69e102c948..e311e019fccc8d0fc67f21a4d144aa27eb07d726 100644
--- a/components/sync/engine_impl/all_status.cc
+++ b/components/sync/engine_impl/all_status.cc
@@ -100,6 +100,11 @@ void AllStatus::OnThrottledTypesChanged(ModelTypeSet throttled_types) {
   status_.throttled_types = throttled_types;
 }
 
+void AllStatus::OnBackedOffTypesChanged(ModelTypeSet backed_off_types) {
+  ScopedStatusLock lock(this);
+  status_.backed_off_types = backed_off_types;
+}
+
 void AllStatus::OnMigrationRequested(ModelTypeSet) {}
 
 void AllStatus::OnProtocolEvent(const ProtocolEvent&) {}