In order to enable natural scrolling, I checked Natural Scroll option in 'Mouse and Touchpad' in System Settings. This basically sets HorizScrollDelta and VertScrollDelta to negative values (checked using synclient).

In other applications (for example, chromium), twofingerscroll behavior gets reversed and edgescroll behavior remains same. I think this natural scroll behavior is ideal as it is consistent with previous versions of gnome-shell and that's what everyone should be used to.

But, in apps that come with gnome-shell (like nautilus, control-center, documents), only edge scrolling behavior gets reversed while two finger scroll behavior remains same which is exactly opposite to the way it works in other apps. 

Instead of reversing edgescroll, twofingerscroll needs to be reversed in case of gnome apps.

To verify the bug:
1. Go to Mouse and Touchpad and enable Two finger scroll and Natural scrolling.
2. Click on 'Test your settings' and check the scroll behaviour.
3. Check scroll behaviour in external applications (like chromium)