This looks like a copypaste error. security/mixedContent/redirect-https-to-http-iframe-in-main-frame.html is identical to security/mixedContent/redirect-http-to-https-iframe-in-main-frame.html because it loads https://127.0.0.1:8443/security/mixedContent/resources/frame-with-redirect-http-to-https-frame.html. It should be loading https://127.0.0.1:8443/security/mixedContent/resources/frame-with-redirect-https-to-http-frame.html.