Google Cloud Compute X11 Forwarding

I'm setting up a virtualbox instance on Google's Cloud Compute Engine. When I try to ssh in on my terminal with the given command they provide plus the following argument after "ssh"

--ssh-flag=-X

I got the error: "X11 forwarding request failed on channel 0." 

First, I updated /etc/ssh/ssh_config by running sudo [editor] /etc/ssh/ssh_config, uncommenting the following lines and putting "yes" where there was a "no."

   ForwardX11 yes

   ForwardX11Trusted yes

Then, I updated the /etc/ssh/sshd_config file, so that after the other X11 related lines it also said the following:

X11UseLocalhost no

Then, I rebooted the machine (sudo reboot) and redid the ssh command with --ssh-flag=-Y to do X11 forwarding. It worked great!