Move AttachmentStore ownership to datatype

sync/api/attachments/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_API_ATTACHMENTS_ATTACHMENT_STORE_H_
 #define SYNC_API_ATTACHMENTS_ATTACHMENT_STORE_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/memory/scoped_ptr.h"
 #include "sync/api/attachments/attachment.h"
 #include "sync/api/attachments/attachment_id.h"
 #include "sync/base/sync_export.h"
 
 namespace base {
 class RefCountedMemory;
 }  // namespace base
 
 namespace syncer {
 
 class Attachment;
 class AttachmentId;
 
 // A place to locally store and access Attachments.
 //
 // Destroying this object does not necessarily cancel outstanding async
 // operations. If you need cancel like semantics, use WeakPtr in the callbacks.
-class SYNC_EXPORT AttachmentStore {
+class SYNC_EXPORT AttachmentStore : public base::RefCounted<AttachmentStore> {
  public:
   AttachmentStore();
-  virtual ~AttachmentStore();
 
   // TODO(maniscalco): Consider udpating Read and Write methods to support
   // resumable transfers (bug 353292).
 
   enum Result {
     SUCCESS,            // No error, all completed successfully.
     UNSPECIFIED_ERROR,  // An unspecified error occurred for one or more items.
   };
 
   typedef base::Callback<void(const Result&,
@@ skipping 33 matching lines @@
   //
   // This does not remove attachments from the server.
   //
   // |callback| will be invoked when finished. Attempting to drop an attachment
   // that does not exist is not an error. If any of the existing attachment
   // could not be dropped, |callback|'s Result will be UNSPECIFIED_ERROR. When
   // this happens, some or none of the attachments may have been dropped
   // successfully.
   virtual void Drop(const AttachmentIdList& ids,
                     const DropCallback& callback) = 0;
+
+ protected:
+  friend class base::RefCounted<AttachmentStore>;
+  virtual ~AttachmentStore();
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_API_ATTACHMENTS_ATTACHMENT_STORE_H_