Repository: flutter
Issue: [web] keep_alive_test 'KeepAlive render tree description' fails on web.
Labels: team,platform-web,P2,c: tech-debt,team: skip-test,team-web,triaged-web

Part of the [skip test audit](https://github.com/flutter/flutter/issues/86396). The test:

https://github.com/flutter/flutter/blob/d3bdbed4985ca2ab174d65a6f556bd18ac03be5e/packages/flutter/test/widgets/keep_alive_test.dart#L193

Is currently skipped on the web. If we reenable it we get:

```
%  flutter test --platform=chrome --web-renderer=html test/widgets/keep_alive_test.dart 
00:03 +3: KeepAlive render tree description                                                                                                                                                                                                                                                                       
══╡ EXCEPTION CAUGHT BY FLUTTER TEST FRAMEWORK ╞════════════════════════════════════════════════════
The following UnsupportedError was thrown running a test:
Unsupported operation: Platform._operatingSystem

When the exception was thrown, this was the stack:
../dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/errors.dart 251:49     throw_
../dart-sdk/lib/_internal/js_dev_runtime/patch/io_patch.dart 244:5                  _operatingSystem
../dart-sdk/lib/io/platform_impl.dart 56:40                                         get operatingSystem
../dart-sdk/lib/io/platform.dart 64:45                                              get _operatingSystem
../dart-sdk/lib/_internal/js_dev_runtime/private/ddc_runtime/operations.dart 835:8  get
../dart-sdk/lib/io/platform.dart 80:40                                              get operatingSystem
keep_alive_test.dart.js 501:222                                                     <fn>
```

If this is not a bug, but intentional, just add a comment with an `[intended]` tag to indicate that this should always be skipped.

<details><summary>flutter doctor</summary>

```
[✓] Flutter (Channel master, 2.5.0-6.0.pre.28, on macOS 11.5.1 20G80 darwin-x64, locale en)
    • Flutter version 2.5.0-6.0.pre.28 at /Users/darrenaustin/dev/flutter
    • Upstream repository git@github.com:flutter/flutter.git
    • Framework revision d3bdbed498 (20 hours ago), 2021-08-06 17:45:02 -0700
    • Engine revision c0e59bc7b6
    • Dart version 2.14.0 (build 2.14.0-383.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/darrenaustin/Library/Android/sdk
    • Platform android-30, build-tools 30.0.2
    • ANDROID_SDK_ROOT = /Users/darrenaustin/Library/Android/sdk
    • Java binary at: /Applications/Android Studio.app/Contents/jre/jdk/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 12.5.1, Build version 12E507
    • CocoaPods version 1.10.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 4.0)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin version 48.1.2
    • Dart plugin version 193.7361
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b3-6222593)

[✓] IntelliJ IDEA Ultimate Edition (version 2021.2)
    • IntelliJ at /Applications/IntelliJ IDEA.app
    • Flutter plugin version 59.0.4
    • Dart plugin version 212.4746.57

[✓] VS Code (version 1.58.2)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.24.0

[✓] Connected device (2 available)
    • macOS (desktop) • macos  • darwin-x64     • macOS 11.5.1 20G80 darwin-x64
    • Chrome (web)    • chrome • web-javascript • Google Chrome 92.0.4515.131

• No issues found!
```
</details>