iframe-isolation-subframe.html

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<!DOCTYPE HTML>

<meta charset=utf-8>

<body style="margin:0">

<script>

  // Reports this frame's own container-timing entries to the embedder, so that

  // the isolation tests can prove a container paint really happened here rather

  // than proving nothing from parent silence.

  const observer = new PerformanceObserver(function(entryList) {

    const entries = entryList.getEntries();

    parent.postMessage({

      kind: 'child-entries',

      count: entries.length,

      identifier: entries.length > 0 ? entries[0].identifier : null

    }, '*');

});

  observer.observe({entryTypes: ['container']});

  const div = document.createElement('div');

  div.setAttribute('containertiming', 'child_ct');

  const img = document.createElement('img');

  img.src = '/container-timing/resources/square100.png';

  div.appendChild(img);

  document.body.appendChild(div);

</script>

</body>