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chromium/third_party/blink/web_tests/external/wpt/intersection-observer/grow-height-and-scrolled.html 

<!DOCTYPE html>
<meta name="viewport" content="width=device-width,initial-scale=1">
<meta name="help" href="https://crbug.com/40895558">
<script src="/resources/testharness.js"></script>
<script src="/resources/testharnessreport.js"></script>
<script src="./resources/intersection-observer-test-utils.js"></script>

<div id="target" style="background: green">
  <div id="content" style="height: 100vh"></div>
</div>

<script>
var entries = [];
new IntersectionObserver(function(changes) {
  target.style.background = changes[0].isIntersecting ? 'green' : 'red';
  entries = entries.concat(changes);
}, {root: document}).observe(target);

runTestCycle(function() {
  assert_equals(entries.length, 1, "Initial notification");
  runTestCycle(scroll);
  content.style.height = "300vh";
}, "IntersectionObserver should only report intersection change after the target grows height and is scrolled.");

function scroll() {
  runTestCycle(check_no_new_entries);
  window.scrollTo(0, 10000);
}

function check_no_new_entries() {
  assert_equals(entries.length, 1, "No new notifications");
}
</script>