[UWP] App has extra 1x1 offset and root widget is not shown fully

[moko256]

On UWP, app has extra 1x1 offset that is different from window border and root widget is not shown fully.

Steps to Reproduce

I created 1px red rectangle in widget root inner, and 1px green rectangle in that rectangle inner.

1. Run flutter create --platforms=windows,winuwp,web one_border.
2. Write lib/main.dart as follows:

import 'package:flutter/material.dart';

void main() {
  runApp(const MyApp());
}

class MyApp extends StatelessWidget {
  const MyApp({Key? key}) : super(key: key);

  @override
  Widget build(BuildContext context) {
    return Container(
      decoration: BoxDecoration(border: Border.all(color: Colors.red)),
      child: Container(
        decoration: BoxDecoration(border: Border.all(color: Colors.green)),
      ),
    );
  }
}

Screenshots (I does not set background. The background blue is UWP primary color):

	screenshot	left-top (viewing in MS Paint)	right-bottom (viewing in MS Paint)
win32 (what I expected behavior)
winuwp (the actual behavior)

Expected results:
On UWP, the red rectangle in the widget root inner is visible.

Actual results:
On UWP, the red rectangle is not visible fully and only the green rectangle in that rectangle inner is visible.

Logs

Analyzing one_border...
No issues found! (ran in 1.9s)

[✓] Flutter (Channel master, 2.5.0-6.0.pre.21, on Microsoft Windows [Version 10.0.19043.1151], locale ja-JP)
    • Flutter version 2.5.0-6.0.pre.21 at C:\Users\moko256\softwares\flutter
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 40e8620a27 (4 hours ago), 2021-08-06 09:14:50 +0430
    • Engine revision 431ac604da
    • Dart version 2.14.0 (build 2.14.0-383.0.dev)

[✗] Android toolchain - develop for Android devices
    ✗ Unable to locate Android SDK.
      Install Android Studio from: https://developer.android.com/studio/index.html
      On first launch it will assist you in installing the Android SDK components.
      (or visit https://flutter.dev/docs/get-started/install/windows#android-setup for detailed instructions).
      If the Android SDK has been installed to a custom location, please use
      `flutter config --android-sdk` to update to that location.


[✓] Chrome - develop for the web
    • Chrome at C:\Program Files\Google\Chrome\Application\chrome.exe

[✓] Visual Studio - develop for Windows (Visual Studio Community 2019 16.10.3)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\Community
    • Visual Studio Community 2019 version 16.10.31424.327
    • Windows 10 SDK version 10.0.19041.0

[!] Android Studio (not installed)
    • Android Studio not found; download from https://developer.android.com/studio/index.html
      (or visit https://flutter.dev/docs/get-started/install/windows#android-setup for detailed instructions).

[✓] VS Code, 64-bit edition (version 1.59.0)
    • VS Code at C:\Program Files\Microsoft VS Code
    • Flutter extension version 3.24.0

[✓] Connected device (4 available)
    • Windows (desktop)       • windows • windows-x64     • Microsoft Windows [Version 10.0.19043.1151]
    • Windows (UWP) (desktop) • winuwp  • windows-uwp-x64 •
    • Chrome (web)            • chrome  • web-javascript  • Google Chrome 92.0.4515.131
    • Edge (web)              • edge    • web-javascript  • Microsoft Edge 92.0.902.62

! Doctor found issues in 2 categories.

[TahaTesser]

Hi @moko256
Thanks for filing the issue and PR, I can reproduce it

flutter doctor -v

[✓] Flutter (Channel master, 2.5.0-6.0.pre.21, on Microsoft Windows [Version 10.0.22000.120], locale en-US)
    • Flutter version 2.5.0-6.0.pre.21 at C:\Users\Taha\Code\flutter_master
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision 40e8620a27 (9 hours ago), 2021-08-06 09:14:50 +0430
    • Engine revision 431ac604da
    • Dart version 2.14.0 (build 2.14.0-383.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.3)
    • Android SDK at C:\Users\Taha\Code\android-sdk
    • Platform android-30, build-tools 30.0.3
    • ANDROID_SDK_ROOT = C:\Users\Taha\Code\android-sdk
    • Java binary at: C:\Users\Taha\Code\android-studio\jre\bin\java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7249189)
    • 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 16.10.4)
    • Visual Studio at C:\Program Files (x86)\Microsoft Visual Studio\2019\Community
    • Visual Studio Community 2019 version 16.10.31515.178
    • Windows 10 SDK version 10.0.19041.0

[✓] Android Studio (version 2020.3)
    • Android Studio at C:\Users\Taha\Code\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 11.0.10+0-b96-7249189)

[✓] VS Code (version 1.59.0)
    • VS Code at C:\Users\Taha\AppData\Local\Programs\Microsoft VS Code
    • Flutter extension version 3.25.0

[✓] Connected device (5 available)
    • IN2011 (mobile)         • c9d8ee0c • android-arm64   • Android 11 (API 30)
    • Windows (desktop)       • windows  • windows-x64     • Microsoft Windows [Version 10.0.22000.120]
    • Windows (UWP) (desktop) • winuwp   • windows-uwp-x64 •
    • Chrome (web)            • chrome   • web-javascript  • Google Chrome 92.0.4515.131
    • Edge (web)              • edge     • web-javascript  • Microsoft Edge 92.0.902.62

• No issues found!

Thanks

[github-actions]

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