CREDENTIAL: Extend FormData opacity to created Request objects

LayoutTests/http/tests/credentialmanager/passwordcredential-basics.html

Index: LayoutTests/http/tests/credentialmanager/passwordcredential-basics.html
diff --git a/LayoutTests/http/tests/credentialmanager/passwordcredential-basics.html b/LayoutTests/http/tests/credentialmanager/passwordcredential-basics.html
index 2085321baed8b4e9b0bd7c92ae54dd8e39e5ce06..f56f3a76d3d1ac51f5dd3da9cf5244011273427d 100644
--- a/LayoutTests/http/tests/credentialmanager/passwordcredential-basics.html
+++ b/LayoutTests/http/tests/credentialmanager/passwordcredential-basics.html
@@ -76,4 +76,30 @@ test(function() {
         assert_unreached("There should be nothing to iterate here.");
     }
 }, 'Verify properties of opaque FormData.');
+
+function verifyBodyMethodBehavior(t, req, methodName) {
+    req[methodName]().then(
+        t.unreached_func("The 'Body::" + methodName + "()' method should reject."),
+        t.step_func_done(function (e) { assert_equals(e.name, "TypeError"); }));
+}
+
+// TODO(mkwst): 'Body' doesn't yet implement 'formData()'.
+['arrayBuffer', 'blob', 'json', 'text'].forEach(function (methodName) {
+    async_test(function (t) {
+        var credential = new PasswordCredential('id', 'pencil');
+        var fd = credential.toFormData();
+        fd.append('n1', 'v1');
+        fd.append('n2', 'v2');
+        fd.append('n3', 'v3');
+        fd.append('n1', 'v4');
+        fd.append('n2', 'v5');
+        fd.append('n3', 'v6');
+
+        t.step(function () {
+            var r = new Request("http://127.0.0.1:8000", { body: fd, method: "POST" });
+            verifyBodyMethodBehavior(t, r, methodName);
+        });
+
+    }, "Verify behavior of 'Body::" + methodName + "()' for opaque Requests.");
+});
 </script>