### Preflight Checklist

- [X] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/main/CONTRIBUTING.md) for this project.
- [X] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/main/CODE_OF_CONDUCT.md) that this project adheres to.
- [X] I have searched the [issue tracker](https://www.github.com/electron/electron/issues) for a feature request that matches the one I want to file, without success.

### Electron Version

14.0.1

### What operating system are you using?

macOS

### Operating System Version

macOS Big Sur 11.6.1

### What arch are you using?

x64

### Last Known Working Electron version

14.0.0

### Expected Behavior


When `BrowserView.setBackgroundColor` is called with an explicit color, expect the background to be the color selected.

When `BrowserView.setBackgroundColor` is not called, expect the background of the `BrowserView` to be transparent by default; and can see through `BrowserWindow`'s background color.



### Actual Behavior

The `BrowserView` background is always white.

### Testcase Gist URL

https://gist.github.com/kevinlinv/2de60478ffec6a2f18f1ec0fc6f5add9

### Additional Information

Here is a quick recording that reproduces the error.

https://user-images.githubusercontent.com/44967897/140694174-e27aff28-1847-4813-bc46-d9fda6569128.mp4


shell/browser/api/electron_api_web_contents.cc
auto* web_preferences = WebContentsPreferences::From(ontents());
  DCHECK(web_preferences);
  web_preferences->SetIgnoreMenuShortcuts(ignore);
}
void WebContents::SetAudioMuted(bool muted) {
  ontents()->SetAudioMuted(muted);
}
bool WebContents::IsAudioMuted() {
  return ontents()->IsAudioMuted();
}
bool WebContents::IsCurrentlyAudible() {
  return ontents()->IsCurrentlyAudible();
}
#if BUILDFLAG(ENABLE_PRINTING)
void WebContents::OnGetDefaultPrinter(
    base::Value print_settings,
    printing::CompletionCallback print_callback,
    std::u16string device_name,
    bool silent,
     <error, default_printer>
    std::pair<std::string, std::u16string> info) {
   The content::WebContents might be already deleted at this point, and the
   PrintViewManagerElectron class does not do null check.
  if (!ontents()) {
    if (print_callback)
      std::move(print_callback).Run(false, "failed");
    return;
  }
  if (!info.first.empty()) {