The disallow_iframe_embed option doesn't belong to HORIZON_CONFIG but should be described as a variable in local_settings. Closes-Bug: #1942722 Change-Id: I189fbb0a76ba63e16f6c3b6ad9db6f9e0355617f (cherry picked from commit7153d5cdfa) (cherry picked from commit7135e8d99d) (cherry picked from commit03d3469f71)