If the “Auto-resize Guest Display” is greyed out for you, go ahead and reboot your virtual machine and check if the issue is resolved. In case that doesn’t work, go ahead and restart your VirtualBox.

In a win for accessibility, Google's no longer forcing users to drag widget edges to resize them in its latest beta.

In any case, this is a good option to have on your smartphone as long as it doesn't interfere with the existing experience.