### Preflight Checklist
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* [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
#include "shell/browser/api/electron_api_url_loader.h"
#include <algorithm>
#include <map>
#include <memory>
#include <string>
#include <utility>
#include <vector>
#include "base/containers/id_map.h"
#include "gin/handle.h"
#include "gin/object_template_builder.h"
#include "gin/wrappable.h"
#include "mojo/public/cpp/bindings/remote.h"
#include "mojo/public/cpp/system/data_pipe_producer.h"
#include "net/base/load_flags.h"
#include "services/network/public/cpp/resource_request.h"