Bug 1648650 [wpt PR 24351] - [html] Improve coverage for COOP, a=testonly

Automatic update from web-platform-tests
[html] Improve coverage for COOP

--

wpt-commits: a69120f0d95b6ce86479f7254761392471dfde7d
wpt-pr: 24351

testing/web-platform/tests/html/cross-origin-opener-policy/coop-sandbox.https.html

@@ -29,6 +29,19 @@
   }, `<iframe sandbox="${sandboxValue}"> ${document.title}`);
 });
 
+// Verify that the popup does not have sandboxing flags set
+async_test(t => {
+  const frame = document.createElement("iframe");
+  const channel = new BroadcastChannel(token());
+  channel.onmessage = t.step_func_done();
+  t.add_cleanup(() => frame.remove());
+  frame.sandbox = "allow-popups allow-scripts allow-popups-to-escape-sandbox";
+  frame.srcdoc = `<script>
+window.open("resources/coop-coep.py?coop=same-origin&coep=&channel=${channel.name}");
+<\/script>`;
+  document.body.append(frame);
+}, `<iframe sandbox="allow-popups allow-scripts allow-popups-to-escape-sandbox"> ${document.title}`);
+
 async_test(t => {
   const frame = document.createElement("iframe");
   const channel = new BroadcastChannel(token());