Disabled FIELDSET elements should not be focusable.

third_party/WebKit/Source/core/html/HTMLFieldSetElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2004, 2005, 2006, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Alexey Proskuryakov (ap@nypop.com)
  *
  * 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
@@ skipping 85 matching lines @@
 
 void HTMLFieldSetElement::childrenChanged(const ChildrenChange& change)
 {
     HTMLFormControlElement::childrenChanged(change);
     for (HTMLLegendElement& legend : Traversal<HTMLLegendElement>::childrenOf(*this))
         invalidateDisabledStateUnder(legend);
 }
 
 bool HTMLFieldSetElement::supportsFocus() const
 {
-    return HTMLElement::supportsFocus();
+    return HTMLElement::supportsFocus() && !isDisabledFormControl();
 }
 
 const AtomicString& HTMLFieldSetElement::formControlType() const
 {
     DEFINE_STATIC_LOCAL(const AtomicString, fieldset, ("fieldset", AtomicString::ConstructFromLiteral));
     return fieldset;
 }
 
 LayoutObject* HTMLFieldSetElement::createLayoutObject(const ComputedStyle&)
 {
@@ skipping 33 matching lines @@
     }
 }
 
 const FormAssociatedElement::List& HTMLFieldSetElement::associatedElements() const
 {
     refreshElementsIfNeeded();
     return m_associatedElements;
 }
 
 } // namespace