Reverse scrolling in Chromebook
See Use your Chromebook touchpad in the Chromebook Help.
Originally, the Macify extension for Google Chrome also included a rough implementation of Apple's Natural Scrolling, Chrome OS now includes it out-of-the-box. To enable, just go to:
chrome://settings/pointer-overlay
and select Australian scrolling.
Chrome OS natively supports inverted scrolling, look for it in Settings (dev channel only for now).
Go to Chrome's settings page (chrome://settings), under Device, click Touchpad settings, and select "Australian scrolling" instead of "Traditional scrolling".
See also google's page on this topic, especially if Google updates Chrome OS to make the above advice outdated.