Add non-blocking sync code to ProfileSyncService

sync/internal_api/public/sync_manager.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_PUBLIC_SYNC_MANAGER_H_
 #define SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 316 matching lines @@
   // to the syncapi model.
   virtual void SaveChanges() = 0;
 
   // Issue a final SaveChanges, and close sqlite handles.
   virtual void ShutdownOnSyncThread() = 0;
 
   // May be called from any thread.
   virtual UserShare* GetUserShare() = 0;
 
   // Returns an instance of the main interface for non-blocking sync types.
-  virtual syncer::SyncCore* GetSyncCore() = 0;
+  virtual base::WeakPtr<syncer::SyncCore> GetSyncCore() = 0;
 
   // Returns the cache_guid of the currently open database.
   // Requires that the SyncManager be initialized.
   virtual const std::string cache_guid() = 0;
 
   // Reads the nigori node to determine if any experimental features should
   // be enabled.
   // Note: opens a transaction.  May be called on any thread.
   virtual bool ReceivedExperiment(Experiments* experiments) = 0;
 
   // Uses a read-only transaction to determine if the directory being synced has
   // any remaining unsynced items.  May be called on any thread.
   virtual bool HasUnsyncedItems() = 0;
 
   // Returns the SyncManager's encryption handler.
   virtual SyncEncryptionHandler* GetEncryptionHandler() = 0;
 
   // Ask the SyncManager to fetch updates for the given types.
   virtual void RefreshTypes(ModelTypeSet types) = 0;
 
   // Returns any buffered protocol events.  Does not clear the buffer.
   virtual ScopedVector<syncer::ProtocolEvent> GetBufferedProtocolEvents() = 0;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_SYNC_MANAGER_H_