### 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

14.2.0 / 15.3.0 / 16.0.0-beta.6

### What operating system are you using?

macOS

### Operating System Version

macOS Catalina 10.15.7

### What arch are you using?

x64

### Last Known Working Electron version

14.0.0 / 15.0.0-beta.2

### Expected Behavior

`<webview>` element should support trasparency. Check the included Fiddle sample.

### Actual Behavior

`<webview>` element transparency is broken

### Testcase Gist URL

_No response_

### Additional Information
[webview-transparency.zip](https://github.com/electron/electron/files/7464785/webview-transparency.zip)

<img width="912" alt="Screen Shot 2021-11-03 at 1 55 47 AM" src="https://user-images.githubusercontent.com/1281234/139971477-2077f353-c17c-417f-9f13-9c5c52139efa.png">
<img width="912" alt="Screen Shot 2021-11-03 at 1 55 53 AM" src="https://user-images.githubusercontent.com/1281234/139971481-49f8afa5-3024-46ba-9339-33c492ba3677.png">

Related to:
https://github.com/electron/electron/blob/2a2a1a834c7072226e9368f36fe0d22a125803f0/shell/browser/api/electron_api_web_contents.cc#L1461

It regressed in this ranges:
- https://github.com/electron/electron/compare/v14.0.0...v14.0.1 (probably #30819)
- https://github.com/electron/electron/compare/v15.0.0-beta.2...v15.0.0-beta.3 (probably #30777)
shell/browser/api/electron_api_web_contents.cc
auto electron_renderer =
      std::make_unique<mojo::Remote<mojom::ElectronRenderer>>();
  frame_host->GetRemoteInterfaces()->GetInterface(
      electron_renderer->BindNewPipeAndPassReceiver());
  auto* raw_ptr = electron_renderer.get();
  (*raw_ptr)->TakeHeapSnapshot(
      mojo::WrapPlatformFile(base::ScopedPlatformFile(file.TakePlatformFile())),
      base::BindOnce(
          [](mojo::Remote<mojom::ElectronRenderer>* ep,
             gin_helper::Promise<void> promise, bool success) {
            if (success) {
              promise.Resolve();
            } else {
              promise.RejectWithErrorMessage("takeHeapSnapshot failed");
            }
          },
          base::Owned(std::move(electron_renderer)), std::move(promise)));
  return handle;
}
void WebContents::GrantDevicePermission(
    const url::Origin& origin,
    const base::Value* device,
    content::PermissionType permissionType,
    content::RenderFrameHost* render_frame_host) {
  granted_devices_[render_frame_host->GetFrameTreeNodeId()][permissionType]
                  [origin]
                      .push_back(
                          std::make_unique<base::Value>(device->Clone()));
}
std::vector<base::Value> WebContents::GetGrantedDevices(