visual-viewport/viewport-resize-event-on-iframe-show.html

<!doctype html>
<html>
    <head>
        <title>Viewport: Resize Event On Showing Iframe</title>
        <meta charset="utf-8">
        <meta name="viewport" content="width=device-width, minimum-scale=1">
        <script src="/resources/testharness.js"></script>
        <script src="/resources/testharnessreport.js"></script>
        <script>
          async_test(t => {
            document.addEventListener("DOMContentLoaded", () => {
              let iframe = document.querySelector("iframe");
              onload = () => {
                requestAnimationFrame(() => { requestAnimationFrame(() => {
                  // First full rendering update is complete.
                  let resize_event_count = 0;
                  iframe.contentWindow.visualViewport.addEventListener("resize", () => {
                    resize_event_count++;
                  });
                  iframe.style.display = "";
                  iframe.clientWidth;
                  requestAnimationFrame(() => {
                    t.step(() => {
                      assert_equals(resize_event_count, 1);
                      t.done();
                    });
                  }) }); // 2x requestAnimationFrame
                })
              };
            });
          }, "Resize event fired when an iframe is shown.");
        </script>
    </head>
    <body>
        <h1>Viewport: Resize Event On Iframe Size Change</h1>
        <h4>
          Test Description: This test ensures that we fire a resize event when
          an iframe is shown.
        </h4>
        <iframe style="display: none;" srcdoc="<p>Hello, world!</p>"></iframe>
        <div id="log"></div>
    </body>
</html>