How to launch Hangouts Chrome extension via AppleScript?
This works for me in macOS High Sierra:

if running of application "Google Chrome" then
    tell application "System Events" to click menu bar item 1 of menu bar 2 of application process "Chrome"
else
    tell application "Google Chrome"
        activate
        tell active tab of front window
            repeat while (loading)
                delay 0.2
            end repeat
        end tell
    end tell
    tell application "System Events" to click menu bar item 1 of menu bar 2 of application process "Chrome"
end if




Note: The example AppleScript code is just that and does not employ any error handling and is meant only to show one of many ways accomplish a task. The onus is always upon the User to add/use appropriate error handling as needed/wanted.