This seems to be a part of their Phishing & malware alerts, so to turn off:

The following steps will turn of phishing and malware warnings, as well as download warnings.
In the top-right corner of the browser window, click the Chrome menu.
Select Settings.
Click Show advanced settings.
Under "Privacy," uncheck the box "Enable phishing and malware protection."

Would seem to turn it off for all sites, so do browse a bit more carefully if you do decide to disable it.