If you have a Touch Screen Chromebook, it is likely you can flip the screen completely over, making your Chromebook a Tablet.
In Tablet Mode, as you rotate your Chromebook, the screen will Auto Rotate with you.
Click on the Clock
Click on the Auto-rotate button.
Click on the clock then Settings (gear)
2. Click on Device then Displays
3. Click on 0 for Normal (Default) View.