Add per attachment metadata records.

sync/internal_api/public/attachments/on_disk_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_ON_DISK_ATTACHMENT_STORE_H_
 #define SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ON_DISK_ATTACHMENT_STORE_H_
 
 #include "base/files/file_path.h"
 #include "base/memory/ref_counted.h"
 #include "base/threading/non_thread_safe.h"
@@ skipping 29 matching lines @@
   void Read(const AttachmentIdList& ids, const ReadCallback& callback) override;
   void Write(const AttachmentList& attachments,
              const WriteCallback& callback) override;
   void Drop(const AttachmentIdList& ids, const DropCallback& callback) override;
 
   // Opens leveldb database at |path|. It will create directory and database if
   // it doesn't exist.
   Result OpenOrCreate(const base::FilePath& path);
 
  private:
-  std::string MakeDataKeyFromAttachmentId(const AttachmentId& attachment_id);
+  friend class OnDiskAttachmentStoreSpecificTest;
+
+  // Reads single attachment from store. Returns nullptr in case of errors.
+  scoped_ptr<Attachment> ReadSingleAttachment(
+      const AttachmentId& attachment_id);
+  // Writes single attachment to store. Returns false in case of errors.
+  bool WriteSingleAttachment(const Attachment& attachment);
+
+  static std::string MakeDataKeyFromAttachmentId(
+      const AttachmentId& attachment_id);
+  static std::string MakeMetadataKeyFromAttachmentId(
+      const AttachmentId& attachment_id);
 
   scoped_refptr<base::SequencedTaskRunner> callback_task_runner_;
   scoped_ptr<leveldb::DB> db_;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_INTERNAL_API_PUBLIC_ATTACHMENTS_ON_DISK_ATTACHMENT_STORE_H_