We have a few stale comments about getEventModifierState:

https://github.com/facebook/react/blob/663835a43a5a92ff63c3e3b43e4c9ff40dde173b/packages/react-dom/src/events/getEventModifierState.js#L24-L26

IE8 isn't an issue anymore, [but Safari probably still is](https://caniuse.com/#feat=keyboardevent-getmodifierstate). It'd be nice to figure out specifically why we still need this module and update the comment with that info.


/**
 * 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.
 *
 * @flow
 */
/**
 * Translation from modifier key to the associated property in the event.
 * @see http://www.w3.org/TR/DOM-Level-3-Events/#keys-Modifiers
 */
import type {AnyNativeEvent} from 'events/PluginModuleType';
const modifierKeyToProp = {
  Alt: 'altKey',
  Control: 'ctrlKey',
  Meta: 'metaKey',
  Shift: 'shiftKey',
};
function modifierStateGetter(keyArg: string): boolean {