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### Issue Details

* **Electron Version:**
  * Tested with 8.0.0 and v9.0.0-beta.1
* **Operating System:**
  * macOS 10.15.3 (19D76)
* **Last Known Working Electron version:**
  * 7.1.12

### Expected Behavior

`navigator.mediaDevices.enumerateDevices()` should return a list of MediaDevices with a `label` and a `deviceId` property. The `deviceId` property should stay the same across reloads and restarts.

### Actual Behavior
The `deviceId` property changes with every reload/restart.

### To Reproduce
Simply execute `navigator.mediaDevices.enumerateDevices()` in the renderer process and compare the ids of the media devices to a different execution.

See this fork for an example:
https://github.com/codedrift/electron-quick-start

```sh
$ git clone https://github.com/codedrift/electron-quick-start -b media-device-ids
$ npm install
$ npm start || electron .
```

### Additional Information
It seems to work fine in a regular Chrome 80 browser. 

shell/browser/electron_browser_client.cc
if (site_instance_from_affinity) {
    *affinity_site_instance = site_instance_from_affinity;
    return SiteInstanceForNavigationType::FORCE_AFFINITY;
  }
  if (!ShouldForceNewSiteInstance(current_rfh, speculative_rfh, browser_context,
                                  url, has_response_started)) {
    return SiteInstanceForNavigationType::ASK_CHROMIUM;
  }
  
  
  
  
  
  
  
  
  
  
  if (has_response_started) {
    return SiteInstanceForNavigationType::FORCE_CURRENT;
  }
  if (!has_navigation_started) {
    
    
    
    return SiteInstanceForNavigationType::FORCE_NEW;
  }
  return SiteInstanceForNavigationType::FORCE_CANDIDATE_OR_NEW;
}
void ElectronBrowserClient::RegisterPendingSiteInstance(