The Chromebook display is split horizontally where the top portion is magnified such as the image shown below.

This is caused when the Docked magnifier option in the Accessibility settings section is enabled.

Disabling Docked Magnifier

1. Select the wireless icon in the notification area to bring up the Settings menu.
2. Select the down arrow next to the Accessibility icon.
3. This will display the Accessibility menu where you can deselect Docked Magnifier so that it does not have a checkmark next to it. 
4. Once unchecked, the display is back to normal