* Electron Version: 3.0.0-beta.1 or 3.0.0-beta.2
* Operating System (Platform and Version): macOS 10.13 (High Sierra)
* Last known working Electron version: 2.0.4

**Expected Behavior**
When a html5 notification is triggered from the renderer, a toast alert should appear

**Actual behavior**
No toast alert is appearing when a html5 notification is triggered from the renderer

**To Reproduce**
```sh
$ git clone https://github.com/VishwasShashidhar/electron-quick-start -b notifications-3beta
$ npm install
$ npm start || electron .
```
Click on the "send notification" button in the renderer.

**Screenshots**

***Working (2.0.4)***
![electron 2 0 4 notifications](https://user-images.githubusercontent.com/5968790/42554031-ea56866e-8500-11e8-91fe-36f87b4180f9.gif)

***Not Working (3.0.0-beta.2)***
![electron 3 0 0 beta 2 notifications](https://user-images.githubusercontent.com/5968790/42554088-22da29fa-8501-11e8-8ba6-22aa765c5eac.gif)

**Additional Information**
N/A
brightray/browser/platform_notification_service.cc
const SkBitmap& icon,
                              const content::PlatformNotificationData& data,
                              bool audio_muted,
                              bool allowed) {
  if (!notification)
    return;
  if (allowed) {
    brightray::NotificationOptions options;
    options.title = data.title;
    options.msg = data.body;
    options.tag = data.tag;
    options.icon_url = data.icon;
    options.icon = icon;
    options.silent = audio_muted ? true : data.silent;
    options.has_reply = false;
    notification->Show(options);
  } else {
    notification->Destroy();
  }
}
class NotificationDelegateImpl final : public brightray::NotificationDelegate {
 public:
  explicit NotificationDelegateImpl(const std::string& notification_id)
      : notification_id_(notification_id) {}
  void NotificationDestroyed() override { delete this; }