[Sync] Introduce AttachmentStoreForSync class

sync/internal_api/public/attachments/in_memory_attachment_store.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 SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_IN_MEMORY_ATTACHMENT_STORE_H_
 #define SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_IN_MEMORY_ATTACHMENT_STORE_H_
 
 #include "base/memory/ref_counted.h"
 #include "base/threading/non_thread_safe.h"
 #include "sync/api/attachments/attachment.h"
@@ skipping 15 matching lines @@
                                             public base::NonThreadSafe {
  public:
   InMemoryAttachmentStore(
       const scoped_refptr<base::SequencedTaskRunner>& callback_task_runner);
   ~InMemoryAttachmentStore() override;
 
   // AttachmentStoreBackend implementation.
   void Init(const AttachmentStore::InitCallback& callback) override;
   void Read(const AttachmentIdList& ids,
             const AttachmentStore::ReadCallback& callback) override;
-  void Write(AttachmentStore::AttachmentReferrer referrer,
+  void Write(AttachmentStore::Component component,
              const AttachmentList& attachments,
              const AttachmentStore::WriteCallback& callback) override;
-  void Drop(AttachmentStore::AttachmentReferrer referrer,
-            const AttachmentIdList& ids,
-            const AttachmentStore::DropCallback& callback) override;
+  void SetReference(AttachmentStore::Component component,
+                    const AttachmentIdList& ids) override;
+  void DropReference(AttachmentStore::Component component,
+                     const AttachmentIdList& ids,
+                     const AttachmentStore::DropCallback& callback) override;
   void ReadMetadata(
       const AttachmentIdList& ids,
       const AttachmentStore::ReadMetadataCallback& callback) override;
   void ReadAllMetadata(
-      AttachmentStore::AttachmentReferrer referrer,
+      AttachmentStore::Component component,
       const AttachmentStore::ReadMetadataCallback& callback) override;
 
  private:
   AttachmentMap attachments_;
 
   DISALLOW_COPY_AND_ASSIGN(InMemoryAttachmentStore);
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_IN_MEMORY_ATTACHMENT_STORE_H_