Alternatively, you can use your HOSTS file in Windows to block certain websites. It is also worth mentioning that editing HOSTS file affects all web browsers, not only Google Chrome. The file is located in C:\WINDOWS\system32\drivers\etc directory.
Open your HOSTS file using Notepad.
Ignore lines that start with #. By default there should be only one entry and you shouldn't change it:
This is a reference the local machine by IP address. You can add as many entries as you want to the HOSTS file. Let's say you want to block facebook.com. You just need to add such entries to block:
We are telling our local machine that Facebook actually exists on the local machine and as a result you'll get a blank page instead of facebook.com. Please note that in Windows Vista and 7 you can change HOSTS file only if you have administrative privileges, i.e., open HOSTS file as the administrator. Otherwise, I'm afraid it won't work.
If you want to block pornography, gaming sites or other questionable website by content you should use parental control software or internet filters. My favourites are K9 Web Protection and Net Nanny. You can read more about parental control software here: http://deletemalware.blogspot.com/2011/06/parental-controls-and-internet-filters.html