Repository: flutter
Issue: `getChildSize` returns wrong size in FlowDelegate.
Labels: framework,has reproducible steps,P2,team-framework,triaged-framework,found in release: 3.22,found in release: 3.24

### Steps to reproduce

context.getChildSize return wrong in paintChildren(FlowPaintingContext context) of custom FlowDelegate
expected: (80,80)
actual: (400,400)

i also found some issues with the same situation:
[issues/40206](https://github.com/flutter/flutter/issues/40206)
[issues/31840](https://github.com/flutter/flutter/issues/31840)

### Expected results

is correct
![image](https://github.com/user-attachments/assets/4e1481cc-dab8-4049-b2b3-420090c600d1)


### Actual results

it is wrong
![image](https://github.com/user-attachments/assets/19fed82f-e9a3-4177-8b9a-d09f79513042)

### Code sample

<details open><summary>Code sample</summary>

```dart
import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({super.key});
  @override
  Widget build(BuildContext context) {
    return MaterialApp(
      title: 'Flutter Demo',
      theme: ThemeData(
        colorScheme: ColorScheme.fromSeed(seedColor: Colors.deepPurple),
        useMaterial3: true,
      ),
      home: const MyHomePage(title: 'Flutter Demo Home Page'),
    );
  }
}

class MyHomePage extends StatefulWidget {
  const MyHomePage({super.key, required this.title});
  final String title;

  @override
  State<MyHomePage> createState() => _MyHomePageState();
}

class _MyHomePageState extends State<MyHomePage> {
  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Theme.of(context).colorScheme.inversePrimary,
        title: Text(widget.title),
      ),
      body: Center(
        child: Container(
          width: 400,
          height: 400,
          color: Colors.black45.withAlpha(128),
          child: Flow(
            delegate: TestFlowFlowDelegate(),
            children: [
              Container(width: 80.0, height: 80.0, color: Colors.pink),
              Container(width: 80.0, height: 80.0, color: Colors.yellow),
              Container(width: 80.0, height: 80.0, color: Colors.green),
              Container(width: 80.0, height: 80.0, color: Colors.blue),
            ],
          ),
        ),
      ),
    );
  }
}

class TestFlowFlowDelegate extends FlowDelegate {
  TestFlowFlowDelegate();

  @override
  BoxConstraints getConstraintsForChild(int i, BoxConstraints constraints) {
    print("child constrains $i $constraints");
    return constraints;
  }

  @override
  void paintChildren(FlowPaintingContext context) {
    print("context size: ${context.size}");
    for (int i = 0; i < context.childCount; i++) {
      var sz = context.getChildSize(i)!;
      print("child $i size: $sz");
      context.paintChild(i, transform: Matrix4.translationValues(i * (10 + sz.width), 0, 0.0));
    }
  }

  @override
  bool shouldRepaint(covariant FlowDelegate oldDelegate) {
    return true;
  }
}
```

</details>


### Screenshots or Video

<details open>
<summary>Screenshots / Video demonstration</summary>

[Upload media here]

</details>


### Logs

<details open><summary>Logs</summary>

```console
Performing hot reload...                                                
Reloaded 0 libraries in 128ms (compile: 6 ms, reload: 0 ms, reassemble: 29 ms).

flutter: child constrains 0 BoxConstraints(w=400.0, h=400.0)
flutter: child constrains 1 BoxConstraints(w=400.0, h=400.0)
flutter: child constrains 2 BoxConstraints(w=400.0, h=400.0)
flutter: child constrains 3 BoxConstraints(w=400.0, h=400.0)
flutter: context size: Size(400.0, 400.0)
flutter: child 0 size: Size(400.0, 400.0)
flutter: child 1 size: Size(400.0, 400.0)
flutter: child 2 size: Size(400.0, 400.0)
flutter: child 3 size: Size(400.0, 400.0)
```

</details>


### Flutter Doctor output

<details open><summary>Doctor output</summary>

```console
$ flutter doctor -v
[√] Flutter (Channel stable, 3.22.3, on Microsoft Windows [版本 10.0.19045.4651], locale zh-CN)
    • Flutter version 3.22.3 on channel stable at D:\Flutter\flutter_windows_3.10.5-stable\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision b0850beeb2 (13 days ago), 2024-07-16 21:43:41 -0700
    • Engine revision 235db911ba
    • Dart version 3.4.4
    • DevTools version 2.34.3

[√] Windows Version (Installed version of Windows is version 10 or higher)

[√] Android toolchain - develop for Android devices (Android SDK version 34.0.0)
    • Android SDK at D:\Android\SDK
    • Platform android-34, build-tools 34.0.0
    • ANDROID_HOME = D:\Android\SDK
    • ANDROID_SDK_ROOT = D:\Android\SDK
    • Java binary at: D:\Android\Android Studio\jbr\bin\java
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-b2043.56-9586694)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop Windows apps (Visual Studio Community 2022 17.6.4)
    • Visual Studio at C:\Program Files\Microsoft Visual Studio\2022\Community
    • Visual Studio Community 2022 version 17.6.33815.320
    • Windows 10 SDK version 10.0.22000.0

[√] Android Studio (version 4.0)
    • Android Studio at D:\Android\android-studio-ide-193.6514223-windows\android-studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)

[√] Android Studio (version 2022.2)
    • Android Studio at D:\Android\Android Studio
    • Flutter plugin can be installed from:
       https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
       https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 17.0.6+0-b2043.56-9586694)

[√] Connected device (3 available)
    • Windows (desktop) • windows • windows-x64    • Microsoft Windows [版本 10.0.19045.4651]
    • Chrome (web)      • chrome  • web-javascript • Google Chrome 126.0.6478.185
    • Edge (web)        • edge    • web-javascript • Microsoft Edge 126.0.2592.102
```

</details>