how to assign keyboard shortcut to buried command?
Here is the code : 

tell application "Google Chrome"
    activate

    tell window 1 to tell active tab to print
    tell application "System Events" to tell process "Google Chrome"
        delay 1
        tell window "Print"
            click menu button "PDF"
            delay 1
            try
                click menu item # of menu of menu button "PDF"
            end try
        end tell
    end tell
end tell


Just replace the #with the index of your script in the menu.  (FYI : 1 is Open PDF in Preview, 8 is Save PDF via Messages