Repository: flutter
Issue: [Web]Chrome on iOS ignores Scrollbar Theme
Labels: platform-ios,framework,f: scrolling,platform-web,has reproducible steps,P2,c: parity,found in release: 3.3,found in release: 3.7,team-framework,triaged-framework

For my application I'd like the scrollbar to always show up when content is bigger than the scroll area. 

I have a scrollbar theme setup that works on a deployed web app on Chrome on desktop & Chrome on Android but not in Chrome on iOS.

On Chrome/iOS the scrollbar theme appears to be completely ignored - see screenshots (Chrome on desktop, Chrome on iOS (no scrollbar visible), Chrome on iOS during scrolling (scroll bar shows up ... but with no theme-ing applied).

It's possible to hack around this by wrapping every `ListView` etc. in a `ScrollBar` and setting properties on that local scroll bar. 

<img src="https://user-images.githubusercontent.com/3914073/213931239-6ebee531-a6dc-48b0-89e2-b8cd5749d28c.png" width="300"/>

<img src="https://user-images.githubusercontent.com/3914073/213931243-89dcccc6-2ee7-4f77-a6f4-67ba7cd90513.PNG" width="300" />

<img src="https://user-images.githubusercontent.com/3914073/213931245-3ad956c7-152e-4005-bb09-c8fcbdc57380.PNG" width="300"/>

## Steps to Reproduce

1. Build sample for web and deploy it somewhere so you can access on a mobile device.
2. View deployed build on device.

**Expected results:** 
Scroll bar to use theme (always shown, chonky width).

**Actual results:**
Scroll bar ignores theme (is hidden by default, thickness wrong)

<details>
<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: 'scroll theme bug',
      theme: ThemeData(
        primarySwatch: Colors.blue,
        scrollbarTheme: ScrollbarTheme.of(context).copyWith(
          thumbVisibility: MaterialStateProperty.all(true),
          thickness: MaterialStateProperty.all(20),
        ),
      ),
      home: Container(
        color: Colors.white,
        child: ListView(
          children: [
            ...[for (var i = 1; i <= 30; i++) i].map((e) => Text('$e')).toList()
          ],
        ),
      ),
    );
  }
}
```

</details>

<details>
<summary>Logs</summary>

```
[√] Flutter (Channel beta, 3.7.0-1.4.pre, on Microsoft Windows [Version 10.0.22621.1105], locale en-US)
    • Flutter version 3.7.0-1.4.pre on channel beta at C:\Developer\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 686fe913dc (12 days ago), 2023-01-10 16:14:01 -0800
    • Engine revision ac5c83dd5f
    • Dart version 2.19.0 (build 2.19.0-444.4.beta)
    • DevTools version 2.20.0

[√] Windows Version (Installed version of Windows is version 10 or higher)

[√] Android toolchain - develop for Android devices (Android SDK version 33.0.0)
    • Android SDK at C:\Users\ben\AppData\Local\Android\sdk
    • Platform android-33, build-tools 33.0.0
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 11.0.13+0-b1751.21-8125866)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[√] Visual Studio - develop for Windows (Visual Studio Community 2019 16.11.15)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\Community
    • Visual Studio Community 2019 version 16.11.32510.428
    • Windows 10 SDK version 10.0.19041.0

[√] Android Studio (version 2021.3)
[√] Connected device (5 available)
    • Pixel 3 (mobile)             • 89RX0E6CW     • android-arm64  • Android 12 (API 31)
    • sdk gphone64 x86 64 (mobile) • emulator-5554 • android-x64    • Android 13 (API 33) (emulator)
    • Windows (desktop)            • windows       • windows-x64    • Microsoft Windows [Version 10.0.22621.1105]
    • Chrome (web)                 • chrome        • web-javascript • Google Chrome 109.0.5414.75
    • Edge (web)                   • edge          • web-javascript • Microsoft Edge 106.0.1370.47

[√] HTTP Host Availability
    • All required HTTP hosts are available

• No issues found!
```

</details>