Fix keyboard_hot_restart_ios flakes (#168518)

The keyboard hot restart test does these steps:

1. It launches an app that forces the keyboard to be visible
2. It checks that the keyboard is visible by examining the app's logs
3. It updates the app to no longer force the keyboard to be visible and
hot restarts the app
4. It checks that the keyboard is no longer visible by examining the
app's logs

Previously, the test app printed the keyboard status whenever the app
rebuilt. The test would move on as soon as it saw a log that indicates
the keyboard was in the expected state. However, since the app could log
the keyboard's visibility _before_ the Dart VM was available, hot
restart commands could be ignored (or at least, that's my theory from
the DeviceLab logs).

Now, the test app prints the keyboard status non-stop. The test now
waits until the Dart VM is available before checking if the logs
indicate the keyboard is open. Also, the test now waits until the hot
restart has completed before checking if the keyboard is closed. In
theory, this should ensure that hot restart does not happen until after
the Dart VM is available.

Follow-up to: https://github.com/flutter/flutter/pull/167013
Part of: https://github.com/flutter/flutter/issues/10713

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant documentation (doc comments with `///`).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

If you need help, consider asking for advice on the #hackers-new channel
on [Discord].

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dev/devicelab/lib/tasks/keyboard_hot_restart_test.dart

@@ -66,14 +66,22 @@ TaskFunction createKeyboardHotRestartTest({
         final String newContents = oldContents.replaceFirst(forceKeyboardOff, forceKeyboardOn);
         mainFile.writeAsStringSync(newContents);
 
-        section('Launch app and wait for keyboard to be visible');
+        section('Launch app');
 
-        TestState state = TestState.waitUntilKeyboardOpen;
+        bool success = false;
+        TestState state = TestState.waitUntilDartVmAvailable;
 
         final int exitCode = await runApp(
           options: <String>['-d', deviceIdOverride!],
           onLine: (String line, Process process) {
-            if (state == TestState.waitUntilKeyboardOpen) {
+            if (state == TestState.waitUntilDartVmAvailable) {
+              if (!line.contains('A Dart VM Service') || !line.contains('is available at')) {
+                return;
+              }
+
+              section('Wait until keyboard is visible');
+              state = TestState.waitUntilKeyboardOpen;
+            } else if (state == TestState.waitUntilKeyboardOpen) {
               if (!line.contains('flutter: Keyboard is open')) {
                 return;
               }
@@ -84,10 +92,15 @@ TaskFunction createKeyboardHotRestartTest({
                 forceKeyboardOff,
               );
               mainFile.writeAsStringSync(newContents);
-
-              section('Hot restart the app');
               process.stdin.writeln('R');
 
+              section('Wait until the app hot restarts');
+              state = TestState.waitUntilHotRestart;
+            } else if (state == TestState.waitUntilHotRestart) {
+              if (!line.contains('Restarted application in ')) {
+                return;
+              }
+
               section('Wait until the keyboard is no longer visible');
               state = TestState.waitUntilKeyboardClosed;
             } else if (state == TestState.waitUntilKeyboardClosed) {
@@ -97,6 +110,7 @@ TaskFunction createKeyboardHotRestartTest({
 
               // Quit the app. This makes the 'flutter run' process exit.
               process.stdin.writeln('q');
+              success = true;
             }
           },
         );
@@ -104,6 +118,10 @@ TaskFunction createKeyboardHotRestartTest({
         if (exitCode != 0) {
           return TaskResult.failure('flutter run exited with non-zero exit code: $exitCode');
         }
+
+        if (!success) {
+          return TaskResult.failure('Test did not complete successfully');
+        }
       } finally {
         mainFile.writeAsStringSync(oldContents);
       }
@@ -113,7 +131,12 @@ TaskFunction createKeyboardHotRestartTest({
   };
 }
 
-enum TestState { waitUntilKeyboardOpen, waitUntilKeyboardClosed }
+enum TestState {
+  waitUntilDartVmAvailable,
+  waitUntilKeyboardOpen,
+  waitUntilHotRestart,
+  waitUntilKeyboardClosed,
+}
 
 Future<void> createAppProject() async {
   await exec(path.join(flutterDirectory.path, 'bin', 'flutter'), <String>[

dev/integration_tests/keyboard_hot_restart/lib/main.dart

@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+import 'dart:async';
+
 import 'package:flutter/material.dart';
 
 // If true, the app autofocuses a text field, making the software keyboard visible.
@@ -11,8 +13,27 @@ import 'package:flutter/material.dart';
 // //dev/devicelab/lib/tasks/keyboard_hot_restart_test.dart
 const bool forceKeyboard = true;
 
+bool? keyboardVisible;
+
 void main() {
   runApp(const MyApp());
+  unawaited(printKeyboardState());
+}
+
+Future<void> printKeyboardState() async {
+  while (true) {
+    await Future<void>.delayed(const Duration(seconds: 1));
+    if (keyboardVisible == null) {
+      continue;
+    }
+
+    // Print whether the keyboard is visible or not.
+    // If you change this line, update the test as well.
+    // See:
+    // //dev/devicelab/lib/tasks/keyboard_hot_restart_test.dart
+    // ignore: avoid_print
+    print('Keyboard is ${keyboardVisible! ? 'open' : 'closed'}');
+  }
 }
 
 class MyApp extends StatelessWidget {
@@ -31,12 +52,7 @@ class MyHomePage extends StatelessWidget {
   Widget build(BuildContext context) {
     final EdgeInsets insets = MediaQuery.of(context).viewInsets;
 
-    // Print whether the keyboard is visible or not.
-    // If you change this line, update the test as well.
-    // See:
-    // //dev/devicelab/lib/tasks/keyboard_hot_restart_test.dart
-    // ignore: avoid_print
-    print('Keyboard is ${insets.bottom > 0 ? 'open' : 'closed'}');
+    keyboardVisible = insets.bottom > 0;
 
     return const Scaffold(body: Center(child: TextField(autofocus: forceKeyboard)));
   }