### 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
frame_subscriber_.reset();
}
void WebContents::StartDrag(const gin_helper::Dictionary& item,
                            gin::Arguments* args) {
  base::FilePath file;
  std::vector<base::FilePath> files;
  if (!item.Get("files", &files) && item.Get("file", &file)) {
    files.push_back(file);
  }
  v8::Local<v8::Value> icon_value;
  if (!item.Get("icon", &icon_value)) {
    gin_helper::ErrorThrower(args->isolate())
        .ThrowError("'icon' parameter is required");
    return;
  }
  NativeImage* icon = nullptr;
  if (!NativeImage::TryConvertNativeImage(args->isolate(), icon_value, &icon) ||
      icon->image().IsEmpty()) {
    return;
  }
   Start dragging.
  if (!files.empty()) {
    base::CurrentThread::ScopedNestableTaskAllower allow;
    DragFileItems(files, icon->image(), ontents()->GetNativeView());
  } else {
    gin_helper::ErrorThrower(args->isolate())
        .ThrowError("Must specify either 'file' or 'files' option");
  }
}
v8::Local<v8::Promise> WebContents::CapturePage(gin::Arguments* args) {