- Electron version: 0.36.12
- Operating system: OSX

There are two problems with `expirationDate`.
### First Problem

`expirationDate` is not returned on non-session cookies.

``` javascript
// not setting session here so it should default to false
var obj = {
  name: 'foo',
  value: 'bar',
  path: '/',
  expirationDate: 2093792393, // 20 years in the future
  url: 'http://localhost/'
}

var cookies = win.webContents.session.cookies

cookies.set(obj, function(err){
  cookies.get({name: "foo"}), function(err, cookies){
    cookies[0].name === 'foo' // => true
    cookies[0].session === false // => true

    // we're missing the expirationDate property!
    cookies[0].expirationDate === undefined // => true
  })
})
```
### Second Problem

When a cookie is marked as a `session` cookie the `expirationDate` property is returned as `0` but it should not be returned at all.

``` javascript
var obj = {
  name: 'foo',
  value: 'bar',
  path: '/',
  session: true, // marking session as true
  url: 'http://localhost/'
}

var cookies = win.webContents.session.cookies

cookies.set(obj, function(err){
  cookies.get({name: "foo"}), function(err, cookies){
    // per the docs this should not have the
    // expirationDate property but it does
    // https://github.com/electron/electron/blob/master/docs/api/session.md#sescookiesgetfilter-callback
    cookies[0].expirationDate === 0 // => true
  })
})
```

atom/browser/api/atom_api_cookies.cc
#include "atom/browser/api/atom_api_cookies.h"
#include "atom/common/native_mate_converters/callback.h"
#include "atom/common/native_mate_converters/gurl_converter.h"
#include "atom/common/native_mate_converters/value_converter.h"
#include "base/time/time.h"
#include "base/values.h"
#include "content/public/browser/browser_context.h"
#include "content/public/browser/browser_thread.h"
#include "native_mate/dictionary.h"
#include "native_mate/object_template_builder.h"
#include "net/cookies/cookie_monster.h"
#include "net/cookies/cookie_store.h"
#include "net/cookies/cookie_util.h"
#include "net/url_request/url_request_context.h"
#include "net/url_request/url_request_context_getter.h"
using content::BrowserThread;
namespace mate {
template<>
struct Converter<atom::api::Cookies::Error> {
  static v8::Local<v8::Value> ToV8(v8::Isolate* isolate,