sync: Support non-blocking initial sync in proto

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 101 matching lines @@
   // Invalidations are notifications the server sends to let us know when other
   // clients have committed data.  We need to contact the sync server (being
   // careful to pass along the "hints" delivered with those invalidations) in
   // order to fetch the update.
   virtual void ScheduleInvalidationNudge(
       const base::TimeDelta& desired_delay,
       syncer::ModelType type,
       scoped_ptr<InvalidationInterface> invalidation,
       const tracked_objects::Location& nudge_location) = 0;
 
+  // Requests a non-blocking initial sync request for the specified type.
+  //
+  // Many types can only complete initial sync while the scheduler is in
+  // configure mode, but a few of them are able to perform their initial sync
+  // while the scheduler is in normal mode.  This non-blocking initial sync
+  // can be requested through this function.
+  virtual void ScheduleInitialSyncNudge(syncer::ModelType model_type) = 0;
+
   // Change status of notifications in the SyncSessionContext.
   virtual void SetNotificationsEnabled(bool notifications_enabled) = 0;
 
   virtual base::TimeDelta GetSessionsCommitDelay() const = 0;
 
   // 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_