### 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
return ontents()->IsCrashed();
}
void WebContents::ForcefullyCrashRenderer() {
  content::RenderWidgetHostView* view =
      ontents()->GetRenderWidgetHostView();
  if (!view)
    return;
  content::RenderWidgetHost* rwh = view->GetRenderWidgetHost();
  if (!rwh)
    return;
  content::RenderProcessHost* rph = rwh->GetProcess();
  if (rph) {
#if defined(OS_LINUX) || defined(OS_CHROMEOS)
     A generic |CrashDumpHungChildProcess()| is not implemented for Linux.
     Instead we send an explicit IPC to crash on the renderer's IO thread.
    rph->ForceCrash();
#else
     Try to generate a crash report for the hung process.
#ifndef MAS_BUILD
    CrashDumpHungChildProcess(rph->GetProcess().Handle());
#endif
    rph->Shutdown(content::RESULT_CODE_HUNG);
#endif
  }
}
void WebContents::SetUserAgent(const std::string& user_agent) {