sync: Move migration signal out of snapshot

sync/sessions/sync_session.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 representing an attempt to synchronize the local syncable data
 // store with a sync server. A SyncSession instance is passed as a stateful
 // bundle throughout the sync cycle.  The SyncSession is not reused across
 // sync cycles; each cycle starts with a new one.
 
 #ifndef SYNC_SESSIONS_SYNC_SESSION_H_
@@ skipping 68 matching lines @@
     virtual void OnSyncProtocolError(
         const SyncProtocolError& sync_protocol_error) = 0;
 
     // Called when the server wants to change the number of hints the client
     // will buffer locally.
     virtual void OnReceivedClientInvalidationHintBufferSize(int size) = 0;
 
     // Called when server wants to schedule a retry GU.
     virtual void OnReceivedGuRetryDelay(const base::TimeDelta& delay) = 0;
 
+    // Called when server requests a migration.
+    virtual void OnReceivedMigrationRequest(ModelTypeSet types) = 0;
+
    protected:
     virtual ~Delegate() {}
   };
 
   // Build a session without a nudge tracker.  Used for poll or configure type
   // sync cycles.
   static SyncSession* Build(SyncSessionContext* context,
                             Delegate* delegate);
   ~SyncSession();
 
@@ skipping 30 matching lines @@
   // Our controller for various status and error counters.
   scoped_ptr<StatusController> status_controller_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncSession);
 };
 
 }  // namespace sessions
 }  // namespace syncer
 
 #endif  // SYNC_SESSIONS_SYNC_SESSION_H_