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

components/sync/engine_impl/cycle/sync_cycle.h

 // Copyright 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_ENGINE_IMPL_CYCLE_SYNC_CYCLE_H_
 #define COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_SYNC_CYCLE_H_
 
 #include <map>
 #include <memory>
 #include <set>
@@ skipping 29 matching lines @@
   class Delegate {
    public:
     // The client was throttled and should cease-and-desist syncing activity
     // until the specified time.
     virtual void OnThrottled(const base::TimeDelta& throttle_duration) = 0;
 
     // Some of the client's types were throttled.
     virtual void OnTypesThrottled(ModelTypeSet types,
                                   const base::TimeDelta& throttle_duration) = 0;
 
+    // Some of the client's types were backed off.
+    virtual void OnTypesBackedOff(ModelTypeSet types) = 0;
+
     // Silenced intervals can be out of phase with individual cycles, so the
     // delegate is the only thing that can give an authoritative answer for
     // "is syncing silenced right now". This shouldn't be necessary very often
     // as the delegate ensures no cycle is started if syncing is silenced.
     // ** Note **  This will return true if silencing commenced during this
     // cycle and the interval has not yet elapsed, but the contract here is
     // solely based on absolute time values. So, this cannot be used to infer
     // that any given cycle _instance_ is silenced.  An example of reasonable
     // use is for UI reporting.
     virtual bool IsCurrentlyThrottled() = 0;
@@ skipping 67 matching lines @@
 
   // Our controller for various status and error counters.
   std::unique_ptr<StatusController> status_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncCycle);
 };
 
 }  // namespace syncer
 
 #endif  // COMPONENTS_SYNC_ENGINE_IMPL_CYCLE_SYNC_CYCLE_H_