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

components/sync_driver/fake_generic_change_processor.cc

 // 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.
 
 #include "components/sync_driver/fake_generic_change_processor.h"
 
 #include "base/location.h"
 #include "base/memory/weak_ptr.h"
 #include "sync/api/syncable_service.h"
 #include "sync/internal_api/public/attachments/attachment_service_impl.h"
 
 namespace sync_driver {
 
 FakeGenericChangeProcessor::FakeGenericChangeProcessor(
     syncer::ModelType type,
     SyncApiComponentFactory* sync_factory)
     : GenericChangeProcessor(type,
                              NULL,
                              base::WeakPtr<syncer::SyncableService>(),
                              base::WeakPtr<syncer::SyncMergeResult>(),
                              NULL,
                              sync_factory,
-                             scoped_refptr<syncer::AttachmentStore>()),
+                             nullptr),
       sync_model_has_user_created_nodes_(true),
       sync_model_has_user_created_nodes_success_(true) {
 }
 
 FakeGenericChangeProcessor::~FakeGenericChangeProcessor() {}
 
 void FakeGenericChangeProcessor::set_sync_model_has_user_created_nodes(
     bool has_nodes) {
   sync_model_has_user_created_nodes_ = has_nodes;
 }
@@ skipping 42 matching lines @@
     syncer::ModelType type,
     syncer::UserShare* user_share,
     DataTypeErrorHandler* error_handler,
     const base::WeakPtr<syncer::SyncableService>& local_service,
     const base::WeakPtr<syncer::SyncMergeResult>& merge_result,
     SyncApiComponentFactory* sync_factory) {
   return processor_.Pass();
 }
 
 }  // namespace sync_driver