### 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
blink::WebMouseWheelEvent mouse_wheel_event;
    if (gin::ConvertFromV8(isolate, input_event, &mouse_wheel_event)) {
      if (IsOffScreen()) {
#if BUILDFLAG(ENABLE_OSR)
        GetOffScreenRenderWidgetHostView()->SendMouseWheelEvent(
            mouse_wheel_event);
#endif
      } else {
         Chromium expects phase info in wheel events (and applies a
         DCHECK to verify it). See: https:crbug.com/756524.
        mouse_wheel_event.phase = blink::WebMouseWheelEvent::kPhaseBegan;
        mouse_wheel_event.dispatch_type =
            blink::WebInputEvent::DispatchType::kBlocking;
        rwh->ForwardWheelEvent(mouse_wheel_event);
         Send a synthetic wheel event with phaseEnded to finish scrolling.
        mouse_wheel_event.has_synthetic_phase = true;
        mouse_wheel_event.delta_x = 0;
        mouse_wheel_event.delta_y = 0;
        mouse_wheel_event.phase = blink::WebMouseWheelEvent::kPhaseEnded;
        mouse_wheel_event.dispatch_type =
            blink::WebInputEvent::DispatchType::kEventNonBlocking;
        rwh->ForwardWheelEvent(mouse_wheel_event);
      }
      return;
    }
  }
  isolate->ThrowException(
      v8::Exception::Error(gin::StringToV8(isolate, "Invalid event object")));
}
void WebContents::BeginFrameSubscription(gin::Arguments* args) {