

### Preflight Checklist
<!-- Please ensure you've completed the following steps by replacing [ ] with [x]-->

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### 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
content::RenderFrameHost* rfh) const {
  auto* web_contents = content::WebContents::FromRenderFrameHost(rfh);
  auto* web_preferences = WebContentsPreferences::From(web_contents);
  std::string affinity;
  if (web_preferences &&
      web_preferences->GetPreference("affinity", &affinity) &&
      !affinity.empty()) {
    affinity = base::ToLowerASCII(affinity);
  }
  return affinity;
}
content::SiteInstance* ElectronBrowserClient::GetSiteInstanceFromAffinity(
    content::BrowserContext* browser_context,
    const GURL& url,
    content::RenderFrameHost* rfh) const {
  std::string affinity = GetAffinityPreference(rfh);
  if (!affinity.empty()) {
    auto iter = site_per_affinities_.find(affinity);
    GURL dest_site = content::SiteInstance::GetSiteForURL(browser_context, url);
    if (iter != site_per_affinities_.end() &&
        IsSameWebSite(browser_context, iter->second, dest_site)) {
      return iter->second;
    }
  }
  return nullptr;
}
void ElectronBrowserClient::ConsiderSiteInstanceForAffinity(