Little things like this keep making the experience on Chromebooks better.
Reshared post from +François Beaufort
We can finally use <Alt>+<Tab> to focus docked windows in the latest Dev Update in Chrome OS.
Whereas it was allowed only for regular windows, we can now simply dock a window by pressing twice <Alt> + [ if we want to dock it to the left for instance and press <Alt>+<Tab> to browse through all windows we have opened (docked included).