### 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* osr_wcv = GetOffScreenWebContentsView();
  return osr_wcv ? osr_wcv->GetFrameRate() : 0;
}
#endif
void WebContents::Invalidate() {
  if (IsOffScreen()) {
#if BUILDFLAG(ENABLE_OSR)
    auto* osr_rwhv = GetOffScreenRenderWidgetHostView();
    if (osr_rwhv)
      osr_rwhv->Invalidate();
#endif
  } else {
    auto* const window = owner_window();
    if (window)
      window->Invalidate();
  }
}
gfx::Size WebContents::GetSizeForNewRenderView(content::WebContents* wc) {
  if (IsOffScreen() && wc == ontents()) {
    auto* relay = NativeWindowRelay::FromWebContents(ontents());
    if (relay) {
      auto* owner_window = relay->GetNativeWindow();
      return owner_window ? owner_window->GetSize() : gfx::Size();
    }
  }
  return gfx::Size();
}
void WebContents::SetZoomLevel(double level) {