There is a "SiteAdvisor for Chrome" available for download from the Google Chrome Extensions list. This has been downloaded by over 16,000 people so far, and I was one of them. What you get is not exactly SiteAdvisor. It dates from 2008, and is "based on McAfee SiteAdvisor". If you have this version of SiteAdvisor installed, I would advise that you uninstall it and re-download SiteAdvisor from McAfee, which should add in the latest Chrome-compatible version (currently 18.104.22.168).
This download is at https://chrome.google.com/extensions/detail/dckheglehcdhpjkdmmmghbgkcdebhhae
The dev.ext download Home Page is at http://www.brothersoft.com/publisher/chrome.dev.ext.html
"chrome.dev.ext" resolves to Brothersoft.com. Their home page is at http://www.brothersoft.com
Brothersoft has a poor reputation. Plenty of allegations of malware in their downloads, although Norton SafeWeb and SiteAdvisor rate the site as safe.
Google SafeBrowsing for Brothersoft says there are/were 15 Trojans on 9 pages (out of 3237 on the site).
Someone has posted a short but scathing article about Brothersoft on Wikipedia : http://en.wikipedia.org/wiki/Brothersoft.com.
The good reviews on SA are all suspiciously similar. Read a few and you'll notice it after a while.
Brothersoft is apparently a Chinese site offering free downloads, games, much of it free. Also comes with added toolbars and (sometimes) Trojans.
Having issued the above warnings, I do not think that there is anything malicious about this Chrome extension. It does a reasonable job of warning about unsafe sites, although it lacks many of the features that SiteAdvisor has in other browsers and seems to be an inferior version of the full McAfee product.