LayoutTests/fast/repaint/css-zoom-iframe-partial-repaint.html

<!DOCTYPE html>
<html>
<head>
<meta charset="utf-8">
<title>Partial repaint inside a CSS-zoomed iframe must propagate a zoom-scaled damage rect to the owner</title>
<style>
  iframe {
    position: absolute;
    left: 0;
    top: 0;
    width: 200px;
    height: 200px;
    border: none;
    zoom: 1.5;
  }
</style>
</head>
<body>
<iframe id="frame" scrolling="no" srcdoc="
  <!DOCTYPE html>
  <style>
    html, body {
      margin: 0;
    }
    #canvas {
      display: block;
    }
  </style>
  <canvas id='canvas' width='80' height='80'></canvas>
"></iframe>
<pre id="repaints"></pre>
<script>
if (window.testRunner) {
    testRunner.dumpAsText();
    testRunner.waitUntilDone();
}

const frame = document.getElementById("frame");

async function test() {
    await new Promise(resolve => frame.addEventListener("load", resolve, { once: true }));
    await new Promise(requestAnimationFrame);
    await new Promise(requestAnimationFrame);

    if (window.internals)
        internals.startTrackingRepaints();

    const canvasContext = frame.contentDocument.getElementById("canvas").getContext("2d");
    canvasContext.fillStyle = "green";
    canvasContext.fillRect(0, 0, 80, 80);

    document.body.offsetTop;

    if (window.internals) {
        document.getElementById("repaints").textContent = internals.repaintRectsAsText();
        internals.stopTrackingRepaints();
    }

    if (window.testRunner)
        testRunner.notifyDone();
}
test();
</script>
</body>
</html>