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chromium/third_party/blink/web_tests/external/wpt/page-visibility/onvisibilitychange.html 

<!doctype html>
<title>onvisibilitychange attribute is a proper event handler</title>
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<div id="log"></div>
<script>
var ast = new async_test("onvisibilitychange attribute is a proper event handler");
function startTest() {
  var iframe1 = document.getElementById("frame1");
  iframe1.contentWindow.document.onvisibilitychange = ast.step_func(function() {
    ast.done();
  });
  frame1.parentNode.removeChild(frame1);
}
</script>
<iframe id="frame1" src='resources/iframe.html'></iframe>