Steps to reproduce:

1. Launch a Flutter multi-window app on Windows (e.g., a sample from the "MVP - The Multi View Playground", or the reference app from [windows] implement regular windows and supporting method channels #157515).
2. Open a new window.
3. Press Alt+F4 to close it.
4. The engine may crash.

Possible cause:

When a key is pressed, FlutterWindowsView::SendKey sends the raw keyboard event to the engine along with a lambda expression as a KeyEventCallback for processing the queued events. Because Alt+F4 immediately closes the window, the view may be destroyed before the callback is invoked. The engine crashes when the callback tries to access already-destroyed objects, such as the FlutterWindowsView itself (its this pointer is captured by the lambda to access FlutterWindowsView::engine_) and the KeyboardManager object, which is owned by the FlutterWindow destroyed with the view.