chromium/third_party/blink/web_tests/printing/subframes-percentage-height.html

<!doctype html>
<title>Test iframe with 100% height content in printing</title>
<script>
    if (window.testRunner)
        testRunner.setPrinting();
</script>
<body style="margin: 0; height:400px">
<iframe frameborder=0 src="data:text/html,<!doctype html>
<style>
  html, body { height: 100%; margin: 0 }
  div { height: 100%; border: 10px solid blue; box-sizing: border-box; }
</style><div></div>"></iframe>