Chromium based browsers freeze when pxt is removed from DOM

The browser's tab freezes when pxt is removed from the DOM.
This happens on chromium based browsers. It does not happen in firefox.

To Reproduce

1. Clone pxt repository (https://github.com/microsoft/pxt.git)
2. Clone pxt sample (https://github.com/microsoft/pxt-sample.git)
   • The folder structure should look like this:
   • bug-report/
     |- pxt/
     |- pxt-sample/
3. Install pxt globally (npm install -g pxt)
4. Install dependencies on both projects
5. Build local pxt (cd pxt; npm run build)
6. Link pxt-sample with local pxt (Deletion of pxt-sample/node_modules/pxt-core/ might be necessary)
   • cd pxt-sample; pxt link ../pxt
7. Serve pxt-sample with custom pxt
   • pxt serve
8. Open on Chrome the controller example
   • http://localhost:3232/controller.html
9. Remove iframe node from browser console

document.getElementById('iframe').parentElement.removeChild(document.getElementById('iframe'))

10. The browser window should be unresponsive at this moment

Desktop:

• OS: macOS Big Sur Version 11.2.1
• Browser:
  • Google Chrome Version 89.0.4389.90 (Official Build) (x86_64)
  • Brave Version 1.21.77 Chromium: 89.0.4389.90 (Official Build) (x86_64)

Additional questions

Should I send a message to pxt before closing?
If so, which one?

Reproduce the freeze using the steps in the issue, serving pxt-sample and opening controller.html in a Chromium-based browser. Start by tracing the iframe removal and its related TypeScript/browser lifecycle code; done means removing the iframe no longer makes the tab unresponsive while Firefox behavior remains unaffected.