html: Add a testcase for submit event reentrancy protection

Specification: whatwg/html#4621

html/semantics/forms/form-submission-0/form-submission-algorithm.html

@@ -18,16 +18,33 @@
  assert_equals(counter, 2);
 }, 'If constructing entry list flag of form is true, then return');
 
-let test10 = async_test('Cannot navigate (after constructing the entry list)');
-test10.step(() => {
+
+async_test(t => {
+ let form = populateForm('<input type=hidden name=n value=v0><input type=submit>');
+ let submitter = form.querySelector('[type=submit]');
+ let iframe = form.previousSibling;
+ form.onsubmit = () => {
+ let hidden = form.querySelector('[type=hidden]');
+ hidden.value = 'inner click()';
+ submitter.click();
+ hidden.value = 'v2';
+ };
+ submitter.click();
+ iframe.onload = t.step_func_done(() => {
+ assert_not_equals(iframe.contentWindow.location.search.indexOf('n=v2'), -1);
+ });
+}, "If form's firing submit event is true, then return");
+
+let test9 = async_test('Cannot navigate (after constructing the entry list)');
+test9.step(() => {
  let form = populateForm('<input name=n1 value=v1>');
  form.onformdata = (e) => { e.target.remove(); };
  let wasLoaded = false;
  let iframe = form.previousSibling;
  // Request to load '/common/dummy.xhtml', and immediately submit the form to
  // the same frame. If the form submission is aborted, the first request
  // will be completed.
- iframe.onload = test10.step_func_done(() => {
+ iframe.onload = test9.step_func_done(() => {
  wasLoaded = true;
  assert_true(iframe.contentWindow.location.search.indexOf('n1=v1') == -1);
  });