chromium/third_party/blink/web_tests/fast/inspector-support/cssURLQuotes.html

<div id="testQuoted1" style="background-image: url(file:///unquoted)"></div>
<div id="testQuoted2" style="background-image: url('file:///quoted')"></div>
<div id="testQuoted3" style="background-image: url('file:///should(Quote)')"></div>
<script>
function test(id, reason) {
    alert(document.getElementById(id).style.getPropertyValue("background-image") + " (" + reason + ")");
}
if (window.testRunner)
    testRunner.dumpAsText();
test("testQuoted1", "URL should be quoted");
test("testQuoted2", "URL should be quoted");
test("testQuoted3", "URL should be quoted");
</script>