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cc @cbracken

I'm not sure that this PR fixes flutter/flutter#92673 because flutter/flutter#92673 has two problems.

• The red box to immediately be replaced with nothing (a grey background)
• Upon resize, the window to be able to be resized, still just showing a grey background.

At the time of writing, this PR seems to solve one. I do think that we want this change, but I'm not sure if we can keep

Fixes: flutter/flutter#92673

in the PR description without solving both issues mentioned in flutter/flutter#92673.

Ping @cbracken @a-wallen

We'll need to author a test for this. I'll give it a shot.

Writing a unit test for this PR in the engine would be easiest via embedding this flutter application

import 'package:flutter/widgets.dart';

void main() async {
  runApp(const Container(color: Color(0xffff0000)));
  runApp(const Container());
}

in a custom entry point for the embedder to consume. However, the engine cannot depend on the framework since the framework depends on the engine. There are two options to test this PR:

1. use dart:ui to emulate the behavior in the above program in a custom dart entrypoint.
2. write integration test in the framework which runs the example above and performs resize in an XCUITest.

The PR above should address the tests for this PR.

test-exempt: test is separate

@knopp May I land this please? Everything looks good to go.

FYI @chinmaygarde, the test for this isn't done.