Actually, the X-Frame-Options is not turn on for docs.google.com domain. SO it, should work, my guess is it could be the JavaScript error somewhere in the code?
This is because the google.com domain has X-Frame-Options turn on.
"X-Frame-Options tells the browser whether you want to allow your site to be framed or not. By preventing a browser from framing your site you can defend against attacks like clickjacking."
Scan results for google.com[
^]