* Electron version: 1.6.2
* Operating system: macOS 10.12

### Expected behavior

Requests sent with the net module should behave one of two ways regarding cookies.
- Either not care about cookies at all, and neither store them nor send them back automatically.
- Or, fully handle cookies, store them when getting a `set-cookie` header, and send them back when necessary, automatically (with the possibility of an option to disable this behaviour)

### Actual behavior

Requests sent with the net module store cookies in the Session used by the request when getting a `set-cookie` header, but do not send them back afterwards.

### How to reproduce

```bash
git clone https://github.com/arantes555/electron-net-cookies-testcase.git && cd electron-net-cookies-testcase
npm i
npm start
```
output: 
```
Server started
REQUEST-HEADERS { 'Accept-Encoding': 'gzip, deflate',
  'Accept-Language': 'fr',
  'User-Agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Electron/1.6.2 Safari/537.36' }
Response SET-COOKIE: undefined
STORED COOKIES: []
REQUEST-HEADERS { 'Accept-Encoding': 'gzip, deflate',
  'Accept-Language': 'fr',
  'User-Agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Electron/1.6.2 Safari/537.36' }
Response SET-COOKIE: a=1,b=1
STORED COOKIES: [{"name":"a","value":"1","domain":"localhost"},{"name":"b","value":"1","domain":"localhost"}]
REQUEST-HEADERS { 'Accept-Encoding': 'gzip, deflate',
  'Accept-Language': 'fr',
  'User-Agent': 'Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_3) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/56.0.2924.87 Electron/1.6.2 Safari/537.36' }
Response SET-COOKIE: a=1,b=1
```

Btw, if I'm reporting multiple issues with the net module these days, it's because I'm working on https://github.com/arantes555/electron-fetch , if you wanna take a look :)
shell/browser/api/electron_api_url_loader.cc
}
  std::string partition;
  gin::Handle<Session> session;
  if (!opts.Get("session", &session)) {
    if (opts.Get("partition", &partition))
      session = Session::FromPartition(args->isolate(), partition);
    else  
      session = Session::FromPartition(args->isolate(), "");
  }
  auto url_loader_factory = session->browser_context()->GetURLLoaderFactory();
  auto* ret =
      new SimpleURLLoaderWrapper(std::move(request), url_loader_factory.get());
  ret->InitWithArgs(args);
  ret->Pin();
  if (!chunk_pipe_getter.IsEmpty()) {
    ret->PinBodyGetter(chunk_pipe_getter);
  }
  return ret;
}
void SimpleURLLoaderWrapper::OnDataReceived(base::StringPiece string_piece,
                                            base::OnceClosure resume) {
  DCHECK_CURRENTLY_ON(content::BrowserThread::UI);
  v8::HandleScope handle_scope(isolate());
  auto array_buffer = v8::ArrayBuffer::New(isolate(), string_piece.size());
  auto backing_store = array_buffer->GetBackingStore();
  memcpy(backing_store->Data(), string_piece.data(), string_piece.size());
  Emit("data", array_buffer);
  std::move(resume).Run();
}
void SimpleURLLoaderWrapper::OnComplete(bool success) {