Support Slot.getAssignedNodes({flatten: true}) in a document tree.

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

 /*
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 37 matching lines @@
 DEFINE_NODE_FACTORY(HTMLSlotElement);
 
 const WillBeHeapVector<RefPtrWillBeMember<Node>> HTMLSlotElement::getAssignedNodesForBinding(const AssignedNodesOptions& options)
 {
     updateDistribution();
     if (options.hasFlatten() && options.flatten())
         return getDistributedNodes();
     return m_assignedNodes;
 }
 
+const WillBeHeapVector<RefPtrWillBeMember<Node>>& HTMLSlotElement::getDistributedNodes()
+{
+    ASSERT(!needsDistributionRecalc());
+    if (isInShadowTree())
+        return m_distributedNodes;
+
+    // A slot is unlikely to be used outside of a shadow tree.
+    // We do not need to optimize this case in most cases.
+    // TODO(hayato): If this path causes a performance issue, we should move
+    // ShadowRootRaraDate::m_descendantSlots into TreeScopreRareData-ish and
+    // update the distribution code so it considers a document tree too.
+    clearDistribution();
+    for (Node& child : NodeTraversal::childrenOf(*this)) {
+        if (isHTMLSlotElement(child))
+            m_distributedNodes.appendVector(toHTMLSlotElement(child).getDistributedNodes());
+        else
+            m_distributedNodes.append(&child);
+    }
+    return m_distributedNodes;
+}
+
 void HTMLSlotElement::appendAssignedNode(Node& node)
 {
     m_assignedNodes.append(&node);
 }
 
 void HTMLSlotElement::appendDistributedNode(Node& node)
 {
     m_distributedNodes.append(&node);
 }
 
@@ skipping 112 matching lines @@
 }
 
 DEFINE_TRACE(HTMLSlotElement)
 {
     visitor->trace(m_assignedNodes);
     visitor->trace(m_distributedNodes);
     HTMLElement::trace(visitor);
 }
 
 }