This app was mentioned in 11 comments, with an average of 1.73 upvotes
I hear you... I'd love to be able to do things like this with my various machines.
Unfortunately, the Pixelbook (like most laptops out there) isn't designed with what you want in terms of using it as an external display. The HDMI port can only output rather than input. You might have some success with Android apps that are designed to act as a second screen for the Mac, like iDisplay (https://play.google.com/store/apps/details?id=com.idisplay.virtualscreen) or Air Display 2 (https://play.google.com/store/apps/details?id=com.avatron.airdisplay2). I've never used second screen sharing software before, so YMMV.
I don't know how to go about sharing the keyboard/trackpad, and that's a feature I'd love to have. I keep wishing that Synergy would release a ChromeOS version of its keyboard sharing app, but that doesn't seem to be in the cards right now.
Android tablet would probably be your cheapest solution. I've used one app and it worked pretty well. I'm sure there's other apps as well. https://play.google.com/store/apps/details?id=com.idisplay.virtualscreen
Or an Android device:
> Turn your Android tablet or phone into additional display for your Mac or Windows computer. Increase your personal productivity by extending your computer screen! Perfect tool for multitaskers, iDisplay lets you use your Android as interactive wireless display to give you more screen real estate.
Use it as a second monitor- ~~https://play.google.com/store/apps/details?id=com.idisplay.virtualscreen&hl=en~~ http://spacedesk.ph/
Seconding iDisplay. It works best over USB but over local network works as well.
https://play.google.com/store/apps/details?id=com.idisplay.virtualscreen
If it works for you