### Preflight Checklist
<!-- Please ensure you've completed the following steps by replacing [ ] with [x]-->

* [x] I have read the [Contributing Guidelines](https://github.com/electron/electron/blob/master/CONTRIBUTING.md) for this project.
* [x] I agree to follow the [Code of Conduct](https://github.com/electron/electron/blob/master/CODE_OF_CONDUCT.md) that this project adheres to.
* [x] I have searched the issue tracker for an issue that matches the one I want to file, without success.

### Issue Details

* **Electron Version:**
  8.0.1
* **Operating System:**
  macOS 10.14.6

### Expected Behavior
Send a request with `referer` header. It's worked with Node's `http/https` module, but failed when I change to `net.request`.

### Actual Behavior
No referer header

### To Reproduce
```js
ses.protocol.interceptStreamProtocol("https", (request, callback) => {
	const resp = sendRequestWithNetRequest({
       url: request.url,
       method: request.method,
	   headers: {
			...request.headers,
			referer: request.referrer  // only referrer has been ignored!!
       }
    })
    callback({
        data: resp.body,
        statusCode: resp.statusCode,
        headers: resp.headers
      });
});
```

shell/browser/api/electron_api_url_loader.cc
std::unique_ptr<network::ResourceRequest> request,
    network::mojom::URLLoaderFactory* url_loader_factory)
    : id_(GetAllRequests().Add(this)) {
  
  
  request->render_frame_id = id_;
  
  
  auto request_body = std::move(request->request_body);
  auto* request_ref = request.get();
  loader_ =
      network::SimpleURLLoader::Create(std::move(request), kTrafficAnnotation);
  if (request_body) {
    request_ref->request_body = std::move(request_body);
  }
  loader_->SetAllowHttpErrorResults(true);
  loader_->SetOnResponseStartedCallback(base::BindOnce(
      &SimpleURLLoaderWrapper::OnResponseStarted, base::Unretained(this)));
  loader_->SetOnRedirectCallback(base::BindRepeating(
      &SimpleURLLoaderWrapper::OnRedirect, base::Unretained(this)));
  loader_->SetOnUploadProgressCallback(base::BindRepeating(
      &SimpleURLLoaderWrapper::OnUploadProgress, base::Unretained(this)));
  loader_->SetOnDownloadProgressCallback(base::BindRepeating(
      &SimpleURLLoaderWrapper::OnDownloadProgress, base::Unretained(this)));
  loader_->DownloadAsStream(url_loader_factory, this);
}
void SimpleURLLoaderWrapper::Pin() {