Tests that if iframe is loaded and then deleted, inspector could still show its content. Note that if iframe.src is changed to "javascript:'...some html...'" after loading, then we have different codepath, hence two tests;
http://127.0.0.1:8000/devtools/network/resources/resource.php
resource.type: document
resource.content after requesting content: Hello world
http://127.0.0.1:8000/devtools/network/resources/resource.php
resource.type: document
resource.content after requesting content: Hello world