The browser-process notifications are either missing or reusing images from the last notification. The reason is simple: In [atom_api_notification, we set the](base::TimeTicks::Now()) `icon_url` to `GURL()`, but in the notification presenter, [we assume an okay and unique path](https://github.com/electron/electron/blob/master/brightray/browser/win/notification_presenter_win.cc#L68-L73).

* Electron version: 1.7+
* Operating system: Windows

### Expected behavior
Notifications should contain the passed icon

### Actual behavior
Notifications contain either no or the last passed icon

### How to reproduce
Use browser-process notifications and attach an image on Windows 10 as icon. Now, send another notification with a different image. Observe how the first icon is shown.

brightray/browser/win/notification_presenter_win.cc
std::vector<unsigned char> png_data;
  if (!gfx::PNGCodec::EncodeBGRASkBitmap(bitmap, false, &png_data))
    return false;
  char* data = reinterpret_cast<char*>(&png_data[0]);
  int size = static_cast<int>(png_data.size());
  return base::WriteFile(path, data, size) == size;
}
}  
NotificationPresenter* NotificationPresenter::Create() {
  auto version = base::win::GetVersion();
  if (version < base::win::VERSION_WIN8)
    return new NotificationPresenterWin7;
  if (!WindowsToastNotification::Initialize())
    return nullptr;
  std::unique_ptr<NotificationPresenterWin> presenter(
      new NotificationPresenterWin);
  if (!presenter->Init())
    return nullptr;
  return presenter.release();
}
NotificationPresenterWin::NotificationPresenterWin() {