Issue #2532 - Align dialog submission triggered by form.submit() with the spec.

Submission in click handler of submit button should not be deferred
per https://html.spec.whatwg.org/multipage/form-control-infrastructure.html#submit-dialog

See Bug 1719872

dom/html/HTMLFormElement.cpp

@@ -676,16 +676,6 @@ HTMLFormElement::DoSubmit(WidgetEvent* aEvent)
 
   mSubmitInitiatedFromUserInput = EventStateManager::IsHandlingUserInput();
 
-  if(mDeferSubmission) {
-    // we are in an event handler, JS submitted so we have to
-    // defer this submission. let's remember it and return
-    // without submitting
-    mPendingSubmission = submission;
-    // ensure reentrancy
-    mIsSubmitting = false;
-    return NS_OK;
-  }
-
   //
   // perform the submission
   //
@@ -709,6 +699,17 @@ HTMLFormElement::DoSubmit(WidgetEvent* aEvent)
           submission->GetAsDialogSubmission()) {
     return SubmitDialog(dialogSubmission);
   }
+
+  if(mDeferSubmission) {
+    // we are in an event handler, JS submitted so we have to
+    // defer this submission. let's remember it and return
+    // without submitting
+    mPendingSubmission = submission;
+    // ensure reentrancy
+    mIsSubmitting = false;
+    return NS_OK;
+  }
+
   return SubmitSubmission(submission);
 }