Support slots' fallback contents in focus navigation

third_party/WebKit/Source/core/dom/shadow/SlotScopedTraversal.cpp

 // Copyright 2016 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "core/dom/shadow/SlotScopedTraversal.h"
 
 #include "core/dom/Element.h"
 #include "core/dom/ElementTraversal.h"
 #include "core/html/HTMLSlotElement.h"
 
@@ skipping 64 matching lines @@
         }
     }
     return nullptr;
 }
 
 bool SlotScopedTraversal::isSlotScoped(const Element& current)
 {
     return SlotScopedTraversal::nearestAncestorAssignedToSlot(current);
 }
 
+HTMLSlotElement* SlotScopedTraversal::findFallbackScopeOwnerSlot(const Element& current)
+{
+    Element* parent = const_cast<Element*>(current.parentElement());
+    while (parent) {
+        if (isHTMLSlotElement(parent))
+            return toHTMLSlotElement(parent)->getAssignedNodes().isEmpty() ? toHTMLSlotElement(parent) : nullptr;
+        parent = parent->parentElement();
+    }
+    return nullptr;
+}
+
+bool SlotScopedTraversal::isSlotFallbackScoped(const Element& current)
+{
+    return SlotScopedTraversal::findFallbackScopeOwnerSlot(current);
+}
+
 } // namespace blink