Keep track of which attachments are referenced by which sync entries.

sync/api/attachments/attachment_service.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_SERVICE_H_
 #define SYNC_API_ATTACHMENTS_ATTACHMENT_SERVICE_H_
 
 #include "base/basictypes.h"
 #include "base/callback.h"
 #include "base/memory/scoped_ptr.h"
@@ skipping 20 matching lines @@
     GET_UNSPECIFIED_ERROR,  // An unspecified error occurred.
   };
 
   typedef base::Callback<
       void(const GetOrDownloadResult&, scoped_ptr<AttachmentMap> attachments)>
       GetOrDownloadCallback;
 
   // The result of a DropAttachments operation.
   enum DropResult {
     DROP_SUCCESS,            // No error, all attachments dropped.
-    DROP_UNSPECIFIED_ERROR,  // An unspecified error occurred.
+    DROP_UNSPECIFIED_ERROR,  // An unspecified error occurred. Some or all
+                             // attachments may not have been dropped.
   };
 
   typedef base::Callback<void(const DropResult&)> DropCallback;
 
+  // The result of a StoreAttachments operation.
+  enum StoreResult {
+    STORE_SUCCESS,            // No error, all attachments stored (at least
+                              // locally).
+    STORE_UNSPECIFIED_ERROR,  // An unspecified error occurred. Some or all
+                              // attachments may not have been stored.
+  };
+
+  typedef base::Callback<void(const StoreResult&)> StoreCallback;
+
   AttachmentService();
   virtual ~AttachmentService();
 
   // See SyncData::GetOrDownloadAttachments.
   virtual void GetOrDownloadAttachments(
       const AttachmentIdList& attachment_ids,
       const GetOrDownloadCallback& callback) = 0;
 
   // See SyncData::DropAttachments.
   virtual void DropAttachments(const AttachmentIdList& attachment_ids,
                                const DropCallback& callback) = 0;
 
-  // This method should be called when a SyncData is about to be added to the
-  // sync database so we have a chance to persist the Attachment locally and
-  // schedule it for upload to the sync server.
-  virtual void OnSyncDataAdd(const SyncData& sync_data) = 0;
+  // Store |attachments| on device and (eventually) upload them to the server.
+  //
+  // Invokes |callback| once the attachments have been written to device
+  // storage.
+  virtual void StoreAttachments(const AttachmentList& attachments,
+                                const StoreCallback& callback) = 0;
 
   // This method should be called when a SyncData is about to be deleted from
   // the sync database so we can remove any unreferenced attachments from local
   // storage.
   virtual void OnSyncDataDelete(const SyncData& sync_data) = 0;
 
   // This method should be called when a SyncData is about to be updated so we
   // can remove unreferenced attachments from local storage and ensure new
   // attachments are persisted and uploaded to the sync server.
   virtual void OnSyncDataUpdate(const AttachmentIdList& old_attachment_ids,
                                 const SyncData& updated_sync_data) = 0;
 };
 
 }  // namespace syncer
 
 #endif  // SYNC_API_ATTACHMENTS_ATTACHMENT_SERVICE_H_