[Sync] Replace AttachmentIdSet with AttachmentIdList in interfaces.

sync/internal_api/public/read_transaction.h

Index: sync/internal_api/public/read_transaction.h
diff --git a/sync/internal_api/public/read_transaction.h b/sync/internal_api/public/read_transaction.h
index c75d16aad3778143e692d43cc554de886d951023..bdb92cbeb33f218fd4b99b5fcea936af75084521 100644
--- a/sync/internal_api/public/read_transaction.h
+++ b/sync/internal_api/public/read_transaction.h
@@ -46,9 +46,9 @@ class SYNC_EXPORT ReadTransaction : public BaseTransaction {
   void GetDataTypeContext(ModelType type,
                           sync_pb::DataTypeContext* context) const;
 
-  // Clear |id_set| and fill it with the ids of attachments that need to be
+  // Clear |ids| and fill it with the ids of attachments that need to be
   // uploaded to the sync server.
-  void GetAttachmentIdsToUpload(ModelType type, AttachmentIdSet* id_set) const;
+  void GetAttachmentIdsToUpload(ModelType type, AttachmentIdList* ids) const;
 
   // Return the current (opaque) store birthday.
   std::string GetStoreBirthday() const;