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chromium/third_party/blink/web_tests/fast/forms/checkbox/checkbox-indeterminate-checked.html 

<!DOCTYPE html>
<link rel="match" href="checkbox-indeterminate-checked-expected.html">
<body>
<input type="checkbox" id="indeterminateCheckbox" checked>
<script>
indeterminateCheckbox.indeterminate = true;
</script>
</body>