### 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
const std::string& file_system_path) {
  auto file_system_paths = GetAddedFileSystemPaths(ontents);
  return file_system_paths.find(file_system_path) != file_system_paths.end();
}
e
#if BUILDFLAG(ENABLE_ELECTRON_EXTENSIONS)
WebContents::Type GetTypeFromViewType(extensions::mojom::ViewType view_type) {
  switch (view_type) {
    case extensions::mojom::ViewType::kExtensionBackgroundPage:
      return WebContents::Type::kBackgroundPage;
    case extensions::mojom::ViewType::kAppWindow:
    case extensions::mojom::ViewType::kComponent:
    case extensions::mojom::ViewType::kExtensionDialog:
    case extensions::mojom::ViewType::kExtensionPopup:
    case extensions::mojom::ViewType::kBackgroundContents:
    case extensions::mojom::ViewType::kExtensionGuest:
    case extensions::mojom::ViewType::kTabContents:
    case extensions::mojom::ViewType::kInvalid:
      return WebContents::Type::kRemote;
  }
}
#endif
WebContents::WebContents(v8::Isolate* isolate,