Remove tabStop feature

Source/core/dom/ContainerNode.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, 2007, 2008, 2009, 2013 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 1066 matching lines @@
             document().styleEngine().pseudoStateChangedForElement(CSSSelector::PseudoFocus, *toElement(this));
         else if (computedStyle()->affectedByFocus())
             setNeedsStyleRecalc(LocalStyleChange, StyleChangeReasonForTracing::createWithExtraData(StyleChangeReason::PseudoClass, StyleChangeExtraData::Focus));
     }
 
     LayoutTheme::theme().controlStateChanged(*layoutObject(), FocusControlState);
 }
 
 void ContainerNode::setFocus(bool received)
 {
-    // Recurse up the shadow trees to mark shadow hosts if it matches :focus.
-    if (isInShadowTree() && shadowHost()->shadowRoot())
-        shadowHost()->setFocus(received);
-
-    // If this is an author shadow host and indirectly focused (has focused element within
-    // its shadow root), update focus.
-    // TODO(kochi): Handle UA shadow which marks multiple nodes as focused such as
-    // <input type="date"> the same way as author shadow.
-    if (document().focusedElement() && document().focusedElement() != this) {
-        Element* host = toElement(this);
-        if (host->shadowRoot())
-            received = received && host->tabIndex() >= 0 && !host->tabStop();
-    }
-
     if (focused() == received)
         return;
 
     Node::setFocus(received);
 
     focusStateChanged();
 
     if (layoutObject() || received)
         return;
 
@@ skipping 410 matching lines @@
         return true;
 
     if (node->isElementNode() && toElement(node)->shadow())
         return true;
 
     return false;
 }
 #endif
 
 } // namespace blink