chromium/third_party/blink/web_tests/fast/hidpi/resize-corner-hidpi.html

<!DOCTYPE html>
<div>This test passes if the resize corner icon appears high-resolution in HiDPI.</div>
<textarea style="resize: both"></textarea>
<script>
    function finishTest() {
        setTimeout(function() { testRunner.notifyDone(); }, 0);
    }
    if (window.testRunner) {
        testRunner.waitUntilDone();
        testRunner.setBackingScaleFactor(2, finishTest);
    }
</script>