<fieldset> should be ignored in interactive validation

Source/core/html/HTMLFormControlElement.h

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
@@ skipping 59 matching lines @@
     virtual bool isEnumeratable() const override { return false; }
 
     bool isRequired() const;
 
     const AtomicString& type() const { return formControlType(); }
 
     virtual const AtomicString& formControlType() const = 0;
 
     virtual bool canTriggerImplicitSubmission() const { return false; }
 
+    virtual bool isSubmittableElement() { return true; }
+
     // Override in derived classes to get the encoded name=value pair for submitting.
     // Return true for a successful control (see HTML4-17.13.2).
     virtual bool appendFormData(FormDataList&, bool) override { return false; }
     virtual String resultForDialogSubmit();
 
     virtual bool canBeSuccessfulSubmitButton() const { return false; }
     bool isSuccessfulSubmitButton() const;
     virtual bool isActivatedSubmit() const { return false; }
     virtual void setActivatedSubmit(bool) { }
 
@@ skipping 113 matching lines @@
 {
     return element.isFormControlElement();
 }
 
 DEFINE_HTMLELEMENT_TYPE_CASTS_WITH_FUNCTION(HTMLFormControlElement);
 DEFINE_TYPE_CASTS(HTMLFormControlElement, FormAssociatedElement, control, control->isFormControlElement(), control.isFormControlElement());
 
 } // namespace
 
 #endif