Currently, ReactEventListener is a DOM-specific module but it has a generic sounding name that is confusing to contributors (i.e., confusing to me).

Let's rename it to ReactDOMEventListener. This should be pretty easy – just rename the file and update (and re-sort) the imports.

# @philipp-spiess is working on this task.
if (!Object.prototype.hasOwnProperty.call(mountAt, topListenersIDKey)) {
    mountAt[topListenersIDKey] = reactTopListenersCounter++;
    alreadyListeningTo[mountAt[topListenersIDKey]] = {};
  }
  return alreadyListeningTo[mountAt[topListenersIDKey]];
}
var ReactBrowserEventEmitter = Object.assign({}, ReactEventEmitterMixin, {
  /**
   * Injectable event backend
   */
  ReactEventListener: null,
  injection: {
    /**
     * @param {object} ReactEventListener
     */
    injectReactEventListener: function(ReactEventListener) {
      ReactEventListener.setHandleTopLevel(
        ReactBrowserEventEmitter.handleTopLevel,
      );
      ReactBrowserEventEmitter.ReactEventListener = ReactEventListener;
    },
  },