Here is something interesting future feature that is coming to Chrome OS. Virtual display. Since the commit log for this feature is very detailed and provides a pretty neat explanation of what is planned, I will just copy and paste that here.

Add support for a virtual display on ChromeOS

The purpose of this feature is to extend the desktop capture functionality by
allowing the creation of a virtual screen at capture request time. The use case
here is to mimic, with e.g. a Chrome Cast, the behaviour that can be achieved
with a physically connected projector i.e that a presenter can have slides
showing whilst keeping notes on their own private screen.

The “Virtual Screen” appears as entry in the display picker, with a new
DesktopMediaID type. In the DesktopCaptureDeviceAura if an item of this type is
requested for capture the virtual screen is enabled in the DisplayConfigurator
and the resulting Aura root window used for capture.

Gaps:
– How to behave when there is already a 2nd display (just disable the ability
to create a virtual screen?)
– Chrome Cast currently uses getUserMedia directly rather than using
chrome.desktopCapture
– Should there be a new enum value “virtual” in DesktopCaptureSourceType in the
desktopCapture API.
– No thumbnail for the virtual screen as we only create it after the fact.

BUG=None
TEST=Use desktopCapture example extension, choose the Virtual Screen when
prompted and observe a new virtual display is created. When the capture is
stopped observe that the virtual display disappears.

So, you get the idea. A virtual display inside your display. When you are presenting something to your Chromecast or a projector, you can have a display (virtual) on the projected screen, and your own private/original display on the Chromebook.

Source: Chromium Code.