Repository: flutter
Issue: `MediaQuery.of(context).viewInsets.bottom` has unexpected value when keyboard is opened/closed
Labels: platform-android,engine,has reproducible steps,P2,found in release: 2.1,team-android,triaged-android

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## Steps to Reproduce

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I am using `MediaQuery.of(context).viewInsets.bottom` and `WidgetsBinding.instance.window.viewInsets.bottom` to get height of keyboard in flutter

When the keyboard is open `MediaQuery.of(context).viewInsets.bottom` is zero and `WidgetsBinding.instance.window.viewInsets.bottom` is 741.0 that is wrong, the device size is 412x732, so the size keyboard cannot be greater than device, I think the keyboard size is about 280 in my case

**Expected results:** <!-- what did you want to see? -->
`viewInsets.bottom` must be ketboard hieght

**Actual results:** <!-- what did you see? -->
`viewInsets.bottom` has unexpected value

<details>
  <summary>Logs</summary>

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```
No issues found! (ran in 11.6s)
```

<!-- Finally, paste the output of running `flutter doctor -v` here. -->

```
[√] Flutter (Channel stable, 2.0.4, on Microsoft Windows [Version 10.0.18363.1440], locale en-US)
    • Flutter version 2.0.4 at C:\flutter
    • Framework revision b1395592de (10 days ago), 2021-04-01 14:25:01 -0700
    • Engine revision 2dce47073a
    • Dart version 2.12.2

[√] Android toolchain - develop for Android devices (Android SDK version 29.0.2)
    • Android SDK at C:\Users\PC\AppData\Local\Android\Sdk
    • Platform android-30, build-tools 29.0.2
    • ANDROID_HOME = C:\Users\PC\AppData\Local\Android\Sdk
    • Java binary at: C:\Program Files\Android\Android Studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 1.8.0_242-release-1644-b01)
    • All Android licenses accepted.

[√] Chrome - develop for the web
    • Chrome at C:\Program Files (x86)\Google\Chrome\Application\chrome.exe

[√] Android Studio (version 4.1.0)
    • Android Studio at C:\Program Files\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 1.8.0_242-release-1644-b01)

[√] Connected device (3 available)
    • Android SDK built for x86 (mobile) • emulator-5554 • android-x86    • Android 10 (API 29) (emulator)
    • Chrome (web)                       • chrome        • web-javascript • Google Chrome 89.0.4389.114
    • Edge (web)                         • edge          • web-javascript • Microsoft Edge 89.0.774.63

• No issues found!

```

</details>