### 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
WebConbContents::From(content::WebContents* ontents) {
  if (!ontents)
    return nullptr;
  auto* data = static_cast<UserDataLink*>(
      ontents->GetUserData(kElectronApiWebContentsKey));
  return data ? data->ontents.get() : nullptr;
}
 static
gin::HContents> WebContents::FromOrCreate(
    v8::Isolate* isolate,
    content::WebContents* ontents) {
  WebContents* api_ontents = From(ontents);
  if (!api_ontents) {
    api_ontents = new WebContents(isolate, ontents);
    v8::TryCatch try_catch(isolate);
    gin_helper::CallMethod(isolate, api_ontents, "_init");
    if (try_catch.HasCaught()) {
      node::errors::TriggerUncaughtException(isolate, try_catch);
    }
  }
  return gin::CreateHandle(isolate, api_ontents);
}
 static