### 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
base::BindRepeating(&WebContents::OnPaint, base::Unretained(this)));
      params.view = view;
      params.delegate_view = view;
      ontents = content::WebContents::Create(params);
      view->SetWebContents(ontents.get());
    } else {
#endif
      ontents = content::WebContents::Create(params);
#if BUILDFLAG(ENABLE_OSR)
    }
  } else if (IsOffScreen()) {
    bool transparent = false;
    options.Get(options::kTransparent, &transparent);
    content::WebContents::CreateParams params(session->browser_context());
    auto* view = new OffScreenWebContentsView(
        transparent,
        base::BindRepeating(&WebContents::OnPaint, base::Unretained(this)));
    params.view = view;
    params.delegate_view = view;
    ontents = content::WebContents::Create(params);
    view->SetWebContents(ontents.get());
#endif
  } else {
    content::WebContents::CreateParams params(session->browser_context());
    params.initially_hidden = !initially_shown;
    ontents = content::WebContents::Create(params);
  }
  InitWithSessionAndOptions(isolate, std::move(ontents), session, options);
}
void WebContents::InitZoomController(content::WebContents* ontents,