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

components/sync/test/engine/fake_sync_scheduler.h

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef COMPONENTS_SYNC_TEST_ENGINE_FAKE_SYNC_SCHEDULER_H_
 #define COMPONENTS_SYNC_TEST_ENGINE_FAKE_SYNC_SCHEDULER_H_
 
 #include <map>
 #include <memory>
 
@@ skipping 28 matching lines @@
   void ScheduleInitialSyncNudge(ModelType model_type) override;
   void SetNotificationsEnabled(bool notifications_enabled) override;
 
   void OnCredentialsUpdated() override;
   void OnConnectionStatusChange() override;
 
   // SyncCycle::Delegate implementation.
   void OnThrottled(const base::TimeDelta& throttle_duration) override;
   void OnTypesThrottled(ModelTypeSet types,
                         const base::TimeDelta& throttle_duration) override;
+  void OnTypesBackedOff(ModelTypeSet types) override;
   bool IsCurrentlyThrottled() override;
   void OnReceivedShortPollIntervalUpdate(
       const base::TimeDelta& new_interval) override;
   void OnReceivedLongPollIntervalUpdate(
       const base::TimeDelta& new_interval) override;
   void OnReceivedCustomNudgeDelays(
       const std::map<ModelType, base::TimeDelta>& nudge_delays) override;
   void OnReceivedClientInvalidationHintBufferSize(int size) override;
   void OnSyncProtocolError(const SyncProtocolError& error) override;
   void OnReceivedGuRetryDelay(const base::TimeDelta& delay) override;
   void OnReceivedMigrationRequest(ModelTypeSet types) override;
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_TEST_ENGINE_FAKE_SYNC_SCHEDULER_H_