Form submission reentrancy protection for 'submit' and 'invalid' event

Differential Revision: https://phabricator.services.mozilla.com/D53696

bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1551758
gecko-commit: 1f77dd98df61bb0b6c5ce53befbb98635fe4eed8
gecko-integration-branch: autoland
gecko-reviewers: smaug

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

@@ -18,6 +18,21 @@
   assert_equals(counter, 2);
 }, 'If constructing entry list flag of form is true, then return');
 
+test(() => {
+  let form = populateForm('<input><input type=submit>');
+  let submitter1 = form.querySelector('input[type=submit]');
+  let valid = form.elements[0];
+  let counter = 0;
+  valid.oninvalid = () => {
+    ++counter;
+  };
+  form.onsubmit = () => {
+    valid.required = true;
+    submitter1.dispatchEvent(new MouseEvent("click"));
+  };
+  submitter1.dispatchEvent(new MouseEvent("click"));
+  assert_equals(counter, 0);
+}, "If firing submission events flag of form is true, then return");
 
 test(() => {
   let form = populateForm('<input required><input type=submit><button type=submit></button>');