Add preconnect and prefetchDNS to rendering-stub

packages/react-dom/server-rendering-stub.js

@@ -18,6 +18,8 @@ export {default as __SECRET_INTERNALS_DO_NOT_USE_OR_YOU_WILL_BE_FIRED} from './s
 export {
   createPortal,
   flushSync,
+  prefetchDNS,
+  preconnect,
   preload,
   preinit,
 } from './src/server/ReactDOMServerRenderingStub';

packages/react-dom/src/__tests__/react-dom-server-rendering-stub-test.js

@@ -53,6 +53,18 @@ describe('react-dom-server-rendering-stub', () => {
     );
   });
 
+  it('provides preconnect and prefetchDNS exports', async () => {
+    function App() {
+      ReactDOM.preconnect('foo', {crossOrigin: 'use-credentials'});
+      ReactDOM.prefetchDNS('bar');
+      return <div>foo</div>;
+    }
+    const html = ReactDOMFizzServer.renderToString(<App />);
+    expect(html).toEqual(
+      '<link rel="preconnect" href="foo" crossorigin="use-credentials"/><link href="bar" rel="dns-prefetch"/><div>foo</div>',
+    );
+  });
+
   it('provides a stub for createPortal', async () => {
     expect(() => {
       ReactDOM.createPortal();

packages/react-dom/src/server/ReactDOMServerRenderingStub.js

@@ -7,7 +7,12 @@
  * @flow
  */
 
-export {preinit, preload} from 'react-dom-bindings/src/shared/ReactDOMFloat';
+export {
+  preinit,
+  preload,
+  preconnect,
+  prefetchDNS,
+} from 'react-dom-bindings/src/shared/ReactDOMFloat';
 
 export function createPortal() {
   throw new Error(