Disallow tabsToLinks setting to prevent tabbing to anchor with tabIndex.

Source/core/html/HTMLAnchorElement.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Simon Hausmann <hausmann@kde.org>
  * Copyright (C) 2003, 2006, 2007, 2008, 2009, 2010 Apple Inc. All rights reserved.
  *           (C) 2006 Graham Dennis (graham.dennis@gmail.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 145 matching lines @@
     // Links are focusable by default, but only allow links with tabindex or contenteditable to be mouse focusable.
     // https://bugs.webkit.org/show_bug.cgi?id=26856
     if (isLink())
         return HTMLElement::supportsFocus();
 
     return HTMLElement::isMouseFocusable();
 }
 
 bool HTMLAnchorElement::isKeyboardFocusable() const
 {
-    if (!isLink())
-        return HTMLElement::isKeyboardFocusable();
-
     if (!isFocusable())
         return false;
 
+    // If the tab index is set explicitly, ignore the tabsToLinks
+    // setting and empty bounding box check.
+    if (Element::supportsFocus())
+        return HTMLElement::isKeyboardFocusable();
+
     Page* page = document().page();
     if (!page)
         return false;
 
     if (!page->chrome().client().tabsToLinks())
         return false;
 
     if (isInCanvasSubtree())
         return true;
 
@@ skipping 668 matching lines @@
 
     // The precision of current MouseOver trigger is too low to actually trigger preconnects.
     if (motivation == WebKit::WebPreconnectMotivationLinkMouseOver)
         return;
 
     preconnectToURL(url, motivation);
     m_hasIssuedPreconnect = true;
 }
 
 }