From a triage[1] of currently failing WPT resource-timing tests[2], the following WebKit test failures may (or may not be) be related to IFRAMEs: https://wpt.fyi/results/resource-timing/nested-context-navigations-embed.html?label=master&label=experimental&aligned https://wpt.fyi/results/resource-timing/nested-context-navigations-iframe.html?label=master&label=experimental&aligned https://wpt.fyi/results/resource-timing/document-domain-no-impact-loader.sub.html?label=master&label=experimental&aligned https://wpt.fyi/results/resource-timing/cross-origin-status-codes.html?label=master&label=experimental&aligned [1] https://github.com/w3c/resource-timing/issues/233 [2] https://wpt.fyi/results/resource-timing?label=master&label=experimental&aligned
Apologies, ignore the "IFRAME" text -- these tests are not running properly.
<rdar://problem/69369178>