Add non-blocking sync code to ProfileSyncService

sync/internal_api/sync_manager_impl.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.
 
 #ifndef SYNC_INTERNAL_API_SYNC_MANAGER_H_
 #define SYNC_INTERNAL_API_SYNC_MANAGER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 93 matching lines @@
   virtual void OnInvalidatorStateChange(InvalidatorState state) OVERRIDE;
   virtual void OnIncomingInvalidation(
       const ObjectIdInvalidationMap& invalidation_map) OVERRIDE;
   virtual std::string GetOwnerName() const OVERRIDE;
   virtual void AddObserver(SyncManager::Observer* observer) OVERRIDE;
   virtual void RemoveObserver(SyncManager::Observer* observer) OVERRIDE;
   virtual SyncStatus GetDetailedStatus() const OVERRIDE;
   virtual void SaveChanges() OVERRIDE;
   virtual void ShutdownOnSyncThread() OVERRIDE;
   virtual UserShare* GetUserShare() OVERRIDE;
-  virtual syncer::SyncCore* GetSyncCore() OVERRIDE;
+  virtual base::WeakPtr<syncer::SyncCore> GetSyncCore() OVERRIDE;
   virtual const std::string cache_guid() OVERRIDE;
   virtual bool ReceivedExperiment(Experiments* experiments) OVERRIDE;
   virtual bool HasUnsyncedItems() OVERRIDE;
   virtual SyncEncryptionHandler* GetEncryptionHandler() OVERRIDE;
   virtual ScopedVector<syncer::ProtocolEvent>
       GetBufferedProtocolEvents() OVERRIDE;
 
   // SyncEncryptionHandler::Observer implementation.
   virtual void OnPassphraseRequired(
       PassphraseRequiredReason reason,
@@ skipping 249 matching lines @@
   scoped_ptr<SyncEncryptionHandlerImpl> sync_encryption_handler_;
 
   base::WeakPtrFactory<SyncManagerImpl> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncManagerImpl);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_SYNC_MANAGER_H_