

### Preflight Checklist
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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 (!BrowserThread::IsThreadInitialized(BrowserThread::IO) ||
      !base::PostTask(
          FROM_HERE, {BrowserThread::IO},
          base::BindOnce(&SetApplicationLocaleOnIOThread, locale))) {
    g_io_thread_application_locale.Get() = locale;
  }
  *g_application_locale = locale;
}
ElectronBrowserClient::ElectronBrowserClient() {
  DCHECK(!g_browser_client);
  g_browser_client = this;
}
ElectronBrowserClient::~ElectronBrowserClient() {
  DCHECK(g_browser_client);
  g_browser_client = nullptr;
}
content::WebContents* ElectronBrowserClient::GetWebContentsFromProcessID(
    int process_id) {
  
  
  const auto iter = pending_processes_.find(process_id);
  if (iter != std::end(pending_processes_))
    return iter->second;
  
  
  return WebContentsPreferences::GetWebContentsFromProcessID(process_id);
}
bool ElectronBrowserClient::ShouldForceNewSiteInstance(