Reland of Fix FlatTreeTraversal for a slot 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 54 matching lines @@
 }
 
 const HeapVector<Member<Node>> HTMLSlotElement::assignedNodesForBinding(
     const AssignedNodesOptions& options) {
   updateDistribution();
   if (options.hasFlatten() && options.flatten())
     return getDistributedNodes();
   return m_assignedNodes;
 }
 
-const HeapVector<Member<Node>>& HTMLSlotElement::getDistributedNodes() {
-  DCHECK(!needsDistributionRecalc());
-  if (isInShadowTree())
-    return m_distributedNodes;
-
+void HTMLSlotElement::updateDistributedNodesManually() {
+  DCHECK(!supportsDistribution());
   // 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
   // ShadowRoot::m_slotAssignment into TreeScopreRareData-ish and
   // update the distribution code so it considers a document tree too.
   clearDistribution();
   Node* child = NodeTraversal::firstChild(*this);
   while (child) {
     if (!child->isSlotable()) {
       child = NodeTraversal::nextSkippingChildren(*child, this);
       continue;
     }
     if (isHTMLSlotElement(child)) {
       child = NodeTraversal::next(*child, this);
     } else {
       m_distributedNodes.append(child);
       child = NodeTraversal::nextSkippingChildren(*child, this);
     }
   }
+}
+
+const HeapVector<Member<Node>>& HTMLSlotElement::getDistributedNodes() {
+  DCHECK(!needsDistributionRecalc());
+  if (!supportsDistribution())
+    updateDistributedNodesManually();
   return m_distributedNodes;
 }
 
 void HTMLSlotElement::appendAssignedNode(Node& hostChild) {
   DCHECK(hostChild.isSlotable());
   m_assignedNodes.append(&hostChild);
 }
 
 void HTMLSlotElement::resolveDistributedNodes() {
   for (auto& node : m_assignedNodes) {
@@ skipping 237 matching lines @@
 
 DEFINE_TRACE(HTMLSlotElement) {
   visitor->trace(m_assignedNodes);
   visitor->trace(m_distributedNodes);
   visitor->trace(m_oldDistributedNodes);
   visitor->trace(m_distributedIndices);
   HTMLElement::trace(visitor);
 }
 
 }  // namespace blink