<!DOCTYPE html>
<style>
#img {content:url('resources/lenna.png')}
</style>
<img id='img' alt='test image'>
<script>
    document.getElementById('img').style.content = "url('ImageDoesNotExist')";
    document.getElementById('img').style.content = "url('resources/lenna.png')";
    document.getElementById('img').style.content = "url('ImageDoesNotExist')";
</script>
<p>crbug.com/516239: images set by content: url() should behave correctly with alt text.