sync: Gracefully handle very early shutdown

sync/engine/sync_scheduler.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.
 //
 // A class to schedule syncer tasks intelligently.
 #ifndef SYNC_ENGINE_SYNC_SCHEDULER_H_
 #define SYNC_ENGINE_SYNC_SCHEDULER_H_
 
 #include <string>
 
@@ skipping 57 matching lines @@
   // scheduled tasks from the old mode may still run.
   virtual void Start(Mode mode) = 0;
 
   // Schedules the configuration task specified by |params|. Returns true if
   // the configuration task executed immediately, false if it had to be
   // scheduled for a later attempt. |params.ready_task| is invoked whenever the
   // configuration task executes.
   // 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).
   //
   // NOTE: |desired_delay| is best-effort. If a nudge is already scheduled to
   // depart earlier than Now() + delay, the scheduler can and will prefer to
   // batch the two so that only one nudge is sent (at the earlier time). Also,
   // as always with delayed tasks and timers, it's possible the task gets run
   // any time after |desired_delay|.
 
@@ skipping 30 matching lines @@
   // Called when credentials are updated by the user.
   virtual void OnCredentialsUpdated() = 0;
 
   // Called when the network layer detects a connection status change.
   virtual void OnConnectionStatusChange() = 0;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_ENGINE_SYNC_SCHEDULER_H_