react/packages/react-devtools-shared/src/devtools/index.js

// @flow

import type {FrontendBridge} from 'react-devtools-shared/src/bridge';

type Shell = {|
  connect: (callback: Function) => void,
  onReload: (reloadFn: Function) => void,
|};

export function initDevTools(shell: Shell) {
  shell.connect((bridge: FrontendBridge) => {
    // TODO ...
  });
}