As of Chrome v30 if you have an http page configured as the URL in a Salesforce Web Tab you will be greated with a blank page.
Checking the developer console shows that the content has been blocked.
[blocked] The page at https://na5.salesforce.com/servlet/servlet.Integration?lid=01r700000000001&ic=1 ran insecure content from http://localhost:60000/site/SalesforceLanding.aspx?SessionId=00D70000000000….
The best solution is to switch the iframe page to use SSL (HTTPS) and you won't have any further issues.
If the iframe is only for development purposes you can temporarily bypass this security check using a small shield that appears on the right of the address bar and selecting "load unsafe script"