UserAgent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10_12_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/61.0.3163.100 Safari/537.36

Steps to reproduce the problem:
In the advertising world the most common issue seen is malware injected on user's computer through malicious ads. Hence, to restrict what an ad can do on a page, iframe sandbox facilitates good controls and a very helpful enhancement to have would be an attribute that can disallow forced file downloads.

What is the expected behavior?
With 

What went wrong?
This is an enhancement request for iframe sandbox.

Did this work before? N/A 

Chrome version: 61.0.3163.100  Channel: n/a
OS Version: OS X 10.12.6
Flash Version: