sync: Gracefully handle very early shutdown

sync/engine/sync_scheduler_impl.h

Index: sync/engine/sync_scheduler_impl.h
diff --git a/sync/engine/sync_scheduler_impl.h b/sync/engine/sync_scheduler_impl.h
index b8dcce9767788ec411a0ca805c1dad7b9deadb94..8492463b5307ff594c63b001819cb26023ea156d 100644
--- a/sync/engine/sync_scheduler_impl.h
+++ b/sync/engine/sync_scheduler_impl.h
@@ -54,7 +54,7 @@ class SYNC_EXPORT_PRIVATE SyncSchedulerImpl
   virtual void Start(Mode mode) OVERRIDE;
   virtual bool ScheduleConfiguration(
       const ConfigurationParams& params) OVERRIDE;
-  virtual void RequestStop() OVERRIDE;
+  virtual void Stop() OVERRIDE;
   virtual void ScheduleLocalNudge(
       const base::TimeDelta& desired_delay,
       ModelTypeSet types,
@@ -181,9 +181,6 @@ class SYNC_EXPORT_PRIVATE SyncSchedulerImpl
   // Determines if we're allowed to contact the server right now.
   bool CanRunNudgeJobNow(JobPriority priority);
 
-  // 'Impl' here refers to real implementation of public functions.
-  void StopImpl();
-
   // If the scheduler's current state supports it, this will create a job based
   // on the passed in parameters and coalesce it with any other pending jobs,
   // then post a delayed task to run it.  It may also choose to drop the job or