chromium/third_party/blink/web_tests/external/wpt/performance-timeline/resources/include-frames-subframe.html

<!DOCTYPE html>

<head>
</head>
<!--
  This html is embedded as a sub-frame in include-frames-originA-B-A.html,
  include-frames-originA-B-B.html and include-frames-originA-A-A.html. Once embedded,
  this would take a url parameter named origin which is the origin of the child frame
  this html is to load in step 3 listed below.
  It does,
  1, waits for load.
  2, creates a single mark performance entry.
  3, creates and loads a child frame, and waits for it to load.
  4. verify entries obtained from this frame.
-->

<body>
  <script>
    (async () => {
      // Wait for load.
      await new Promise(resolve => window.addEventListener("load", resolve));

      // Mark.
      performance.mark("mark_subframe");

      // Create and load an iframe and wait for load.
      await new Promise(resolve => {
        const childFrame = document.createElement('iframe');

        childFrame.addEventListener('load', async () => {
          window.parent.postMessage('Load completed', "*");
          resolve();
        });

        childFrame.src = (new URL(document.location)).searchParams.get('origin')
          + '/performance-timeline/resources/child-frame.html';

        document.body.appendChild(childFrame);
      }
      );
    })();
  </script>
</body>