As part of #32329, currently certain metrics of the window object are hardcoded to look at the actual window object.

This is no longer true, once that the app is embedded in a custom element.

Ensure that the following metrics and events are correctly handled:

• Physical size
• Safe zone / padding
• Resize events
• ??? others?

Default behavior

If the hostElement is not passed, everything should behave as it does right now (taking measurements from the window object, etc...)

Docs

• See Cross-platform view information, EngineFlutterWindow section in the design doc