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* Electron version: 1.6.10
* Operating system: Windows 7

### Expected behavior

<!-- What do you think should happen? -->

Notification size should be smaller, similar to the one you can just see in the screenshot below that you can just see the bottom of, behind the large notification.


### Actual behavior

<!-- What actually happens? -->

The new notifications for windows 7 are taking up half of the screen space as seen in the image below:
![image](https://cloud.githubusercontent.com/assets/5689874/26761521/f2eec2c4-4928-11e7-9572-6df74ddb7ad1.png)

I'm running windows in parallels on a mac, so I expect it to be a screen resolution issue (2880x1800)



### How to reproduce

Test notifications on Windows 7 with parallels on a mac, or use Windows with a high screen resolution (e.g. 2880x1800).

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brightray/browser/win/win32_desktop_notifications/desktop_notification_controller.cc
ScreenMetrics metrics;
        auto margin = metrics.Y(toast_margin_<int>);
        int target_pos = 0;
        for (auto&& inst : instances_) {
            if (inst.hwnd) {
                auto toast = Toast::Get(inst.hwnd);
                if (toast->IsHighlighted())
                    target_pos = toast->GetVerticalPosition();
                else
                    toast->SetVerticalPosition(target_pos);
                target_pos += toast->GetHeight() + margin;
            }
        }
    }
    
    CheckQueue();
}
DesktopNotificationController::Notification
    DesktopNotificationController::AddNotification(
    std::wstring caption, std::wstring body_text, HBITMAP image) {
    NotificationLink data(this);
    data->caption = move(caption);
    data->body_text = move(body_text);
    data->image = CopyBitmap(image);
    
    Notification ret { *queue_.insert(queue_.end(), move(data)) };
    CheckQueue();
    return ret;
}
void DesktopNotificationController::CloseNotification(