Fetch Metadata: Add a test for <embed> navigated after loading.

@annevk noted in whatwg/fetch#948 (comment)
that it was possible to navigate an `<embed>` after it loads. I think
we should probably figure out how to make that navigation show up with a
destination of `embed` and a mode of `no-cors`.

Surprisingly, that seems to be what we're sending via Fetch Metadata.
I suspect it's not what the underlying `fetch()` API would show in a
service worker.

Bug: 1011763
Change-Id: I0156b2b1b467c914b15f6af50dfa37ce74db6c62

fetch/metadata/embed.tentative.https.sub.html

@@ -65,4 +65,76 @@
       document.body.appendChild(e);
     })
   }, "Cross-Site embed");
+
+  promise_test(t => {
+    return new Promise((resolve, reject) => {
+      let key = "post-embed-same-origin" + nonce;
+
+      let e = document.createElement('embed');
+      e.src = "/common/blank.html";
+      e.addEventListener("load", _ => {
+        e.addEventListener("load", e => {
+          let expected = {"dest":"embed", "site":"same-origin", "user":"", "mode":"no-cors"};
+          fetch("/fetch/metadata/resources/record-header.py?retrieve=true&file=" + key)
+            .then(response => response.text())
+            .then(text => assert_header_equals(text, expected))
+            .then(_ => resolve())
+            .catch(e => reject(e));
+        }, { once: true });
+
+        // Navigate the existing `<embed>`
+        window.frames[window.length - 1].location = "https://{{host}}:{{ports[https][0]}}/fetch/metadata/resources/record-header.py?file=" + key;
+      }, { once: true });
+
+      document.body.appendChild(e);
+    })
+  }, "Navigate to same-origin embed");
+
+  promise_test(t => {
+    return new Promise((resolve, reject) => {
+      let key = "post-embed-same-origin" + nonce;
+
+      let e = document.createElement('embed');
+      e.src = "/common/blank.html";
+      e.addEventListener("load", _ => {
+        e.addEventListener("load", e => {
+          let expected = {"dest":"embed", "site":"same-site", "user":"", "mode":"no-cors"};
+          fetch("/fetch/metadata/resources/record-header.py?retrieve=true&file=" + key)
+            .then(response => response.text())
+            .then(text => assert_header_equals(text, expected))
+            .then(_ => resolve())
+            .catch(e => reject(e));
+        }, { once: true });
+
+        // Navigate the existing `<embed>`
+        window.frames[window.length - 1].location = "https://{{hosts[][www]}}:{{ports[https][0]}}/fetch/metadata/resources/record-header.py?file=" + key;
+      }, { once: true });
+
+      document.body.appendChild(e);
+    })
+  }, "Navigate to same-site embed");
+
+  promise_test(t => {
+    return new Promise((resolve, reject) => {
+      let key = "post-embed-same-origin" + nonce;
+
+      let e = document.createElement('embed');
+      e.src = "/common/blank.html";
+      e.addEventListener("load", _ => {
+        e.addEventListener("load", e => {
+          let expected = {"dest":"embed", "site":"cross-site", "user":"", "mode":"no-cors"};
+          fetch("/fetch/metadata/resources/record-header.py?retrieve=true&file=" + key)
+            .then(response => response.text())
+            .then(text => assert_header_equals(text, expected))
+            .then(_ => resolve())
+            .catch(e => reject(e));
+        }, { once: true });
+
+        // Navigate the existing `<embed>`
+        window.frames[window.length - 1].location = "https://{{hosts[alt][www]}}:{{ports[https][0]}}/fetch/metadata/resources/record-header.py?file=" + key;
+      }, { once: true });
+
+      document.body.appendChild(e);
+    })
+  }, "Navigate to cross-site embed");
 </script>