chromium/third_party/blink/web_tests/editing/spelling/spelling-huge-text.html

<!doctype html>
<script src="../../resources/testharness.js"></script>
<script src="../../resources/testharnessreport.js"></script>
<script src="../assert_selection.js"></script>
<script src="spellcheck_test.js"></script>

<script>
// TODO(xiaochengh): Remove this test, and introduce more carefully designed
// benchmarks to perf_tests/editing/spelling. crbug.com/699335
const longText = 'Good good good good good good good good good good good good good. '.repeat(600);
spellcheck_test(
    `<div contenteditable>zz zz zz. ${longText}</div>`,
    document => document.querySelector('div').focus(),
    `<div contenteditable>#zz# #zz# #zz#. ${longText}</div>`,
    'Spellchecking long text does not freeze the page.');
</script>