[react-dom] Enforce small gap between completed navigation and default Transition indicator (#33354)

Author: eps1lon

fixtures/flight/src/App.js

@@ -12,6 +12,7 @@ import Button from './Button.js';
 import Form from './Form.js';
 import {Dynamic} from './Dynamic.js';
 import {Client} from './Client.js';
+import {Navigate} from './Navigate.js';
 
 import {Note} from './cjs/Note.js';
 
@@ -89,6 +90,7 @@ export default async function App({prerender}) {
           <Note />
           <Foo>{dedupedChild}</Foo>
           <Bar>{Promise.resolve([dedupedChild])}</Bar>
+          <Navigate />
         </Container>
       </body>
     </html>

fixtures/flight/src/Navigate.js

@@ -0,0 +1,40 @@
+'use client';
+
+import * as React from 'react';
+import Container from './Container.js';
+
+export function Navigate() {
+  /** Repro for https://issues.chromium.org/u/1/issues/419746417 */
+  function provokeChromeCrash() {
+    React.startTransition(async () => {
+      console.log('Default transition triggered');
+
+      await new Promise(resolve => {
+        setTimeout(
+          () => {
+            history.pushState(
+              {},
+              '',
+              `?chrome-crash-419746417=${performance.now()}`
+            );
+          },
+          // This needs to happen before React's default transition indicator
+          // is displayed but after it's scheduled.
+          100 + -50
+        );
+
+        setTimeout(() => {
+          console.log('Default transition completed');
+          resolve();
+        }, 1000);
+      });
+    });
+  }
+
+  return (
+    <Container>
+      <h2>Navigation fixture</h2>
+      <button onClick={provokeChromeCrash}>Provoke Chrome Crash (fixed)</button>
+    </Container>
+  );
+}

packages/react-dom/src/client/ReactDOMDefaultTransitionIndicator.js

@@ -38,7 +38,8 @@ export function defaultOnDefaultTransitionIndicator(): void | (() => void) {
     if (!isCancelled) {
       // Some other navigation completed but we should still be running.
       // Start another fake one to keep the loading indicator going.
-      startFakeNavigation();
+      // There needs to be an async gap to work around https://issues.chromium.org/u/1/issues/419746417.
+      setTimeout(startFakeNavigation, 20);
     }
   }
 
@@ -70,7 +71,7 @@ export function defaultOnDefaultTransitionIndicator(): void | (() => void) {
     }
   }
 
-  // Delay the start a bit in case this is a fast navigation.
+  // Delay the start a bit in case this is a fast Transition.
   setTimeout(startFakeNavigation, 100);
 
   return function () {