The instructions on Google site stated that for Chrome browser:
Copy the URL text starting with chrome-devtools://devtools/remote/serve_rev..., open a new tab, and paste the URL text into the URL field in Chrome.
But I could not see any of that text. (see image)
What have I missed?
Just click on Remote Debugging(AppEngine). That will open the debug console, which should contain that url. If you're on Chrome already though, there's no need to copy the url and open it in a new tab. The point of copying the url is to bring it into Chrome.
Make sure that you also enable scripts. The right most portion of the url bar should have a shield icon. Click on that to enable scripts.