chromium/third_party/blink/web_tests/compositing/iframes/fixed-position-element-in-iframe-enters-viewport.html

<!DOCTYPE html>
<!--
This test verifies that a fixed position element inside an iframe paints when
it comes into view due to the iframe increasing in size.

If this test passes, you should see a green square.
-->
<html>
<head>
    <style>
        #iframe-containing-fixed-position-element {
            background: red;
            width: 100px;
            height: 0;
            border: 0;
        }
    </style>
    <script src="../../resources/run-after-layout-and-paint.js"></script>
    <script>
        if (window.testRunner)
            testRunner.waitUntilDone();

        if (window.internals)
            internals.settings.setPreferCompositingToLCDTextEnabled(true);

        function runTest()
        {
            // Initially, the fixed position element in the iframe will not
            // paint because the iframe has zero height.
            runAfterLayoutAndPaint(function() {
                // Give the iframe a non-zero height. The fixed position element
                // inside the iframe should paint now.
                var iframeElement = document.getElementById("iframe-containing-fixed-position-element");
                iframeElement.style.height = "100px";

                if (window.testRunner)
                    testRunner.notifyDone();
            });
        }
    </script>
</head>
<body onload="runTest()">
    <iframe id="iframe-containing-fixed-position-element" src="resources/subframe-with-fixed-position-element.html"></iframe>
</body>
</html>