chromium/third_party/blink/web_tests/external/wpt/fenced-frame/resources/csp-inner.html

<!DOCTYPE html>
  <script src="utils.js"></script>

  <style>
    body {background-color: red;}
  </style>

  <title>Fenced frame content to test Content Security Policies</title>

  <body>
    <script>
      const [csp_key] = parseKeylist();

      function fail() {
        writeValueToServer(csp_key,
          "FAIL: img-src policy was not honored in fenced frame");
      }

      function pass() {
        // The parent page is going to attempt to pass a
        // style-src: 'none' CSP to the fenced frame. Make sure that
        // the header is not honored.
        const bgcolor = window.getComputedStyle(document.body, null)
                        .getPropertyValue('background-color');

        if (bgcolor != "rgb(255, 0, 0)") {
          writeValueToServer(csp_key,
            "FAIL: style-src policy was passed to fenced frame");
          return;
        }

        writeValueToServer(csp_key, "pass");
      }
    </script>
    <img src="csp.png" id="my_img" onload="fail();" onerror="pass();">
  </body>
</html>