COOP: test iframe sandbox without allow-same-origin

Part of #18354.

html/cross-origin-opener-policy/coop-sandbox.https.html

@@ -5,20 +5,25 @@
 <script src="/common/utils.js"></script> <!-- Use token() to allow running tests in parallel -->
 <div id=log>
 <script>
-async_test(t => {
-  const frame = document.createElement("iframe");
-  const channel = new BroadcastChannel(token());
-  channel.onmessage = t.unreached_func("A COOP popup was created from a sandboxed frame");
-  t.add_cleanup(() => frame.remove());
-  frame.sandbox = "allow-popups allow-scripts allow-same-origin";
-  frame.srcdoc = `<script>
-const popup = window.open("resources/coop-coep.py?coop=same-origin&coep=&channel=${channel.name}");
-<\/script>`;
-  document.body.append(frame);
-  window.onload = t.step_func(() => {
-    t.step_timeout(() => {
-      t.done()
-    }, 1500);
-  });
+[
+  "allow-popups allow-scripts allow-same-origin",
+  "allow-popups allow-scripts",
+].forEach(sandboxValue => {
+  async_test(t => {
+    const frame = document.createElement("iframe");
+    const channel = new BroadcastChannel(token());
+    channel.onmessage = t.unreached_func("A COOP popup was created from a sandboxed frame");
+    t.add_cleanup(() => frame.remove());
+    frame.sandbox = sandboxValue;
+    frame.srcdoc = `<script>
+  const popup = window.open("resources/coop-coep.py?coop=same-origin&coep=&channel=${channel.name}");
+  <\/script>`;
+    document.body.append(frame);
+    window.onload = t.step_func(() => {
+      t.step_timeout(() => {
+        t.done()
+      }, 1500);
+    });
+  }, `<iframe sandbox="${sandboxValue}"> ${document.title}`);
 });
 </script>