### Website or app

google.com

### Repro steps

This started after last update 4.20.0
![image](https://user-images.githubusercontent.com/11052469/137713404-e6702959-7870-46a6-8566-4cfe61d25309.png)
![image](https://user-images.githubusercontent.com/11052469/137713464-c5e478d2-4e9e-4ee4-abdf-83d23c04704b.png)


### How often does this bug happen?

Every time

### DevTools package (automated)

_No response_

### DevTools version (automated)

_No response_

### Error message (automated)

_No response_

### Error call stack (automated)

_No response_

### Error component stack (automated)

_No response_

### GitHub query string (automated)

_No response_
backendDisconnected = true;
  window.removeEventListener('message', handleMessageFromPage);
  window.postMessage(
    {
      source: 'react-devtools-content-script',
      payload: {
        type: 'event',
        event: 'shutdown',
      },
    },
    '*',
  );
}
const port = chrome.runtime.connect({
  name: 'content-script',
});
port.onMessage.addListener(handleMessageFromDevtools);
port.onDisconnect.addListener(handleDisconnect);
window.addEventListener('message', handleMessageFromPage);
sayHelloToBackend();
if (!backendInitialized) {
  const intervalID = setInterval(() => {
    if (backendInitialized || backendDisconnected) {
      clearInterval(intervalID);
    } else {
      sayHelloToBackend();
    }
  }, 500);
}