Steps to Reproduce

1. Have a fullscreen-sized GMap widget in a Stack with a toolbar and stuff
2. Have a button launching pushNamed to change routes
3. (Have a custom onGenerateRoute giving normal MaterialPageRoutes, and use flutter_web_plugins to get rid of the hash in the url)
4. Open page with GMap in Chrome or Firefox on Windows
5. Click button

Expected results:

The new page opens, and the GMap on the old page disappears with the old page.

Actual results:

The new page opens, and the GMap quickly reappears on top of the new page after it's done animating its appearance. It will not resize with the browser window anymore, but it will react to dragging etc.

Detailed information:
This does not happen on mobile webbrowsers, and also not on emulated mobile in Chrome after refreshing the page. If I emulate mobile in Chrome, refresh the page, and then quit emulating mobile without refreshing, it does also not occur. I didn't have this issue using flutter_google_maps, so I doubt it's a common iframe issue. This happens on the latest dev and master build (probably others too, can't test my full application there without major adaptations), and my Flutter doctor is all good.