chromium/third_party/blink/web_tests/plugins/webview-plugin-border-radius.html

<!doctype HTML>
<style>
  #plugin {
    width: 150px;
    height: 150px;
    border: 5px solid black;
    border-radius: 20px;
  }
</style>
<embed id="plugin" type="application/x-plugin-placeholder-test"></embed>
<script>
onload = function() {
    if (window.testRunner) {
        testRunner.waitUntilDone();
        // Need to paint two frames in order to allow the plugin to properly load.
        // TODO(chrishtr): find out why and fix.
        requestAnimationFrame(function() {
            requestAnimationFrame(function() {
                requestAnimationFrame(function() {
                    testRunner.notifyDone();
                });
            });
        });
    }
}
</script>