[Sync] Refactor AttachmentStore classes. Introduce concept of referrer.

components/sync_driver/generic_change_processor.h

 // Copyright 2014 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 COMPONENTS_SYNC_DRIVER_GENERIC_CHANGE_PROCESSOR_H_
 #define COMPONENTS_SYNC_DRIVER_GENERIC_CHANGE_PROCESSOR_H_
 
 #include <vector>
 
 #include "base/compiler_specific.h"
@@ skipping 36 matching lines @@
   // Create a change processor for |type| and connect it to the syncer.
   // |attachment_store| can be NULL which means that datatype will not use sync
   // attachments.
   GenericChangeProcessor(
       syncer::ModelType type,
       DataTypeErrorHandler* error_handler,
       const base::WeakPtr<syncer::SyncableService>& local_service,
       const base::WeakPtr<syncer::SyncMergeResult>& merge_result,
       syncer::UserShare* user_share,
       SyncApiComponentFactory* sync_factory,
-      const scoped_refptr<syncer::AttachmentStore>& attachment_store);
+      scoped_ptr<syncer::AttachmentStore> attachment_store);
   ~GenericChangeProcessor() override;
 
   // ChangeProcessor interface.
   // Build and store a list of all changes into |syncer_changes_|.
   void ApplyChangesFromSyncModel(
       const syncer::BaseTransaction* trans,
       int64 version,
       const syncer::ImmutableChangeRecordList& changes) override;
   // Passes |syncer_changes_|, built in ApplyChangesFromSyncModel, onto
   // |local_service_| by way of its ProcessSyncChanges method.
@@ skipping 99 matching lines @@
       attachment_service_weak_ptr_factory_;
   syncer::AttachmentServiceProxy attachment_service_proxy_;
   base::WeakPtrFactory<GenericChangeProcessor> weak_ptr_factory_;
 
   DISALLOW_COPY_AND_ASSIGN(GenericChangeProcessor);
 };
 
 }  // namespace sync_driver
 
 #endif  // COMPONENTS_SYNC_DRIVER_GENERIC_CHANGE_PROCESSOR_H_