Repository: flutter
Issue: Buggy scroll in WebView inside of the PageView 
Labels: platform-ios,a: platform-views,p: webview,package,has reproducible steps,P2,found in release: 2.5,found in release: 2.6,team-ios,triaged-ios

## Steps to Reproduce

<!-- Please include full steps to reproduce so that we can reproduce the problem. -->

1. Execute `flutter run` on the code sample <!-- (see "Code sample" section below) -->

**Expected results:** 
During horizontal/vertical scroll other widgets shouldn't move on the screen.

**Actual results:** 
I have a screen where the webview is on background for showing 3d models. That's why I use `PageView` with WebView inside. During the animation of the PageView, I see artifacts on the iOS platform. Widgets are flickering during scroll/animation. Looks like the 1 rendered frame is with incorrect size. The same code on Android runs well, on iOS looks buggy. See attached video. Looks like a regress of the https://github.com/flutter/flutter/issues/29427 but maybe I am wrong. I tried to use the hard-coded sizes for webview, global keys, even switching pages without animations but nothing works. On Android, everything is ok even with the more complex screen.

<details>
<summary>
Code sample
</summary>

```dart
@override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        backgroundColor: Color(0xFF292A2D),
        title: Text('Edit profile'),
      ),
      body: PageView.builder(
        scrollDirection: Axis.vertical,
        itemCount: 5,
        itemBuilder: (_, i) => const WebView(initialUrl: 'https://google.com'),
      ),
    );
  }
```

</details>

<details>
  <summary>Logs</summary>

```
[assertion] Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}>
[ProcessSuspension] 0x131df9d40 - ProcessAssertion: Failed to acquire RBS assertion 'ConnectionTerminationWatchdog' for process with PID=71511, error: Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}
[assertion] Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}>
[ProcessSuspension] 0x131df9fe0 - ProcessAssertion: Failed to acquire RBS assertion 'ConnectionTerminationWatchdog' for process with PID=71520, error: Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}
[assertion] Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}>
[ProcessSuspension] 0x131df9620 - ProcessAssertion: Failed to acquire RBS assertion 'ConnectionTerminationWatchdog' for process with PID=71522, error: Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}
[assertion] Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}>
[ProcessSuspension] 0x131df90e0 - ProcessAssertion: Failed to acquire RBS assertion 'ConnectionTerminationWatchdog' for process with PID=71523, error: Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}
[assertion] Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}>
[ProcessSuspension] 0x131df8ea0 - ProcessAssertion: Failed to acquire RBS assertion 'ConnectionTerminationWatchdog' for process with PID=71524, error: Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}
[assertion] Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}>
[ProcessSuspension] 0x131df9980 - ProcessAssertion: Failed to acquire RBS assertion 'ConnectionTerminationWatchdog' for process with PID=71526, error: Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}
[assertion] Error acquiring assertion: <Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}>
[ProcessSuspension] 0x131df8540 - ProcessAssertion: Failed to acquire RBS assertion 'ConnectionTerminationWatchdog' for process with PID=71527, error: Error Domain=RBSServiceErrorDomain Code=1 "target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit" UserInfo={NSLocalizedFailureReason=target is not running or doesn't have entitlement com.apple.runningboard.assertions.webkit}
Could not signal service com.apple.WebKit.WebContent: 113: Could not find specified service

```


```
[✓] Flutter (Channel stable, 2.5.3, on macOS 11.6 20G165 darwin-x64, locale en-RU)
    • Flutter version 2.5.3 at /Users/artem/flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 18116933e7 (5 weeks ago), 2021-10-15 10:46:35 -0700
    • Engine revision d3ea636dc5
    • Dart version 2.14.4

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at /Users/artem/Library/Android/sdk
    • Platform android-31, build-tools 30.0.3
    • ANDROID_HOME = /Users/artem/Library/Android/sdk
    • ANDROID_SDK_ROOT = /Users/artem/Library/Android/sdk
    • Java binary at: /Applications/Android Studio 4.2 Preview.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • Xcode 13.0, Build version 13A233
    • CocoaPods version 1.10.1

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2020.3)
    • Android Studio at /Applications/Android Studio 4.2 Preview.app/Contents
    • 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 11.0.10+0-b96-7281165)

[✓] IntelliJ IDEA Community Edition (version 2021.2.2)
    • IntelliJ at /Applications/IntelliJ IDEA CE.app
    • 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

[✓] VS Code (version 1.62.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.28.0

[✓] Connected device (3 available)
    • Android SDK built for x86 (mobile) • emulator-5554             • android-x86    • Android 10 (API 29) (emulator)
    • iPhone 13 Pro (mobile)             • 00008110-00024C4A1A78801E • ios            • iOS 15.1 19B74
    • Chrome (web)                       • chrome                    • web-javascript • Google Chrome 96.0.4664.55

• No issues found!

```

</details>

https://user-images.githubusercontent.com/12301508/142883965-c6491dad-49be-4ebd-b9a1-3e47483a5e4d.MP4