-- upstream: https://github.com/facebook/react/blob/2ba43edc2675380a0f2222f351475bf9d750c6a9/packages/shared/ReactInstanceMap.js
--!strict
--[[*
 * Copyright (c) Facebook, Inc. and its affiliates.
 *
 * This source code is licensed under the MIT license found in the
 * LICENSE file in the root directory of this source tree.
 ]]