* 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
#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 "services/network/public/cpp/resource_request.h"
#include "services/network/public/cpp/simple_url_loader.h"
#include "services/network/public/mojom/chunked_data_pipe_getter.mojom.h"
#include "services/network/public/mojom/url_loader_factory.mojom.h"
#include "shell/browser/api/electron_api_session.h"
#include "shell/browser/electron_browser_context.h"
#include "shell/common/gin_converters/callback_converter.h"
#include "shell/common/gin_converters/gurl_converter.h"
#include "shell/common/gin_converters/net_converter.h"
#include "shell/common/gin_helper/dictionary.h"
#include "shell/common/gin_helper/object_template_builder.h"
#include "shell/common/node_includes.h"
namespace gin {
template <>
struct Converter<network::mojom::HttpRawHeaderPairPtr> {
  static v8::Local<v8::Value> ToV8(