OWA Web Parts not working in 2013 – "This content cannot be displayed in a frame"

A while back in 2013 (Cumulative Update 2) there was a change which causes a header called X-Frame-Options to be inserted into rendered OWA pages.  This header tells browsers to not render content in an iFrame.  This is a security feature which is meant to help prevent click-jacking. There is a WebPartsFrameOptionsType setting on VDIR/MailboxPolicy, which…