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

sync/api/attachments/attachment_service_proxy.h

Index: sync/api/attachments/attachment_service_proxy.h
diff --git a/sync/api/attachments/attachment_service_proxy.h b/sync/api/attachments/attachment_service_proxy.h
index 70856255cfa56d43b445468f7c650186ea858a7b..462cddadea97ac54d63a6a707abb30a4dfb8f05a 100644
--- a/sync/api/attachments/attachment_service_proxy.h
+++ b/sync/api/attachments/attachment_service_proxy.h
@@ -58,7 +58,8 @@ class SYNC_EXPORT AttachmentServiceProxy : public AttachmentService {
       const GetOrDownloadCallback& callback) OVERRIDE;
   virtual void DropAttachments(const AttachmentIdList& attachment_ids,
                                const DropCallback& callback) OVERRIDE;
-  virtual void OnSyncDataAdd(const SyncData& sync_data) OVERRIDE;
+  virtual void StoreAttachments(const AttachmentList& attachment,
+                                const StoreCallback& callback) OVERRIDE;
   virtual void OnSyncDataDelete(const SyncData& sync_data) OVERRIDE;
   virtual void OnSyncDataUpdate(const AttachmentIdList& old_attachment_ids,
                                 const SyncData& updated_sync_data) OVERRIDE;
@@ -89,7 +90,8 @@ class SYNC_EXPORT AttachmentServiceProxy : public AttachmentService {
         const GetOrDownloadCallback& callback) OVERRIDE;
     virtual void DropAttachments(const AttachmentIdList& attachment_ids,
                                  const DropCallback& callback) OVERRIDE;
-    virtual void OnSyncDataAdd(const SyncData& sync_data) OVERRIDE;
+    virtual void StoreAttachments(const AttachmentList& attachment,
+                                  const StoreCallback& callback) OVERRIDE;
     virtual void OnSyncDataDelete(const SyncData& sync_data) OVERRIDE;
     virtual void OnSyncDataUpdate(const AttachmentIdList& old_attachment_ids,
                                   const SyncData& updated_sync_data) OVERRIDE;