sync: Gracefully handle very early shutdown

sync/engine/sync_scheduler.h

Index: sync/engine/sync_scheduler.h
diff --git a/sync/engine/sync_scheduler.h b/sync/engine/sync_scheduler.h
index 923c7be2d95ad6f59698ca52fbcc3bdbc32f3fa9..b31af82791353e6154cc295c95be217fc26c309a 100644
--- a/sync/engine/sync_scheduler.h
+++ b/sync/engine/sync_scheduler.h
@@ -75,11 +75,9 @@ class SYNC_EXPORT_PRIVATE SyncScheduler
   // Note: must already be in CONFIGURATION mode.
   virtual bool ScheduleConfiguration(const ConfigurationParams& params) = 0;
 
-  // Request that any running syncer task stop as soon as possible and
-  // cancel all scheduled tasks. This function can be called from any thread,
-  // and should in fact be called from a thread that isn't the sync loop to
-  // allow preempting ongoing sync cycles.
-  virtual void RequestStop() = 0;
+  // Request that the syncer avoid starting any new tasks and prepare for
+  // shutdown.
+  virtual void Stop() = 0;
 
   // The meat and potatoes. All three of the following methods will post a
   // delayed task to attempt the actual nudge (see ScheduleNudgeImpl).