Make sure to lazyReattach a distributed node if it is already attached

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 121 matching lines @@
 void HTMLSlotElement::appendDistributedNodesFrom(const HTMLSlotElement& other)
 {
     size_t index = m_distributedNodes.size();
     m_distributedNodes.appendVector(other.m_distributedNodes);
     for (const auto& node : other.m_distributedNodes)
         m_distributedIndices.set(node.get(), index++);
 }
 
 void HTMLSlotElement::clearDistribution()
 {
+    // TODO(hayato): Figure out when to call lazyReattachDistributedNodesIfNeeded()
     m_assignedNodes.clear();
     m_distributedNodes.clear();
     m_distributedIndices.clear();
 }
 
+void HTMLSlotElement::saveAndClearDistribution()
+{
+    m_oldDistributedNodes.swap(m_distributedNodes);
+    clearDistribution();
+}
+
 void HTMLSlotElement::dispatchSlotChangeEvent()
 {
     m_slotchangeEventEnqueued = false;
     Event* event = Event::create(EventTypeNames::slotchange);
     event->setTarget(this);
     dispatchScopedEvent(event);
 }
 
 Node* HTMLSlotElement::distributedNodeNextTo(const Node& node) const
 {
@@ skipping 127 matching lines @@
     for (auto& child : NodeTraversal::childrenOf(*this)) {
         if (!child.isSlotable())
             continue;
         if (isHTMLSlotElement(child))
             appendDistributedNodesFrom(toHTMLSlotElement(child));
         else
             appendDistributedNode(child);
     }
 }
 
+void HTMLSlotElement::lazyReattachDistributedNodesIfNeeded()
+{
+    // TODO(hayato): Figure out an exact condition where reattach is required
+    if (m_oldDistributedNodes != m_distributedNodes) {
+        for (auto& node : m_oldDistributedNodes)
+            node->lazyReattachIfAttached();
+        for (auto& node : m_distributedNodes)
+            node->lazyReattachIfAttached();
+    }
+    m_oldDistributedNodes.clear();
+}
+
 void HTMLSlotElement::enqueueSlotChangeEvent()
 {
     if (!m_slotchangeEventEnqueued) {
         Microtask::enqueueMicrotask(WTF::bind(&HTMLSlotElement::dispatchSlotChangeEvent, Persistent<HTMLSlotElement>(this)));
         m_slotchangeEventEnqueued = true;
     }
 
     ShadowRoot* root = containingShadowRoot();
     DCHECK(root);
     DCHECK(root->isV1());
@@ skipping 27 matching lines @@
 
 short HTMLSlotElement::tabIndex() const
 {
     return Element::tabIndex();
 }
 
 DEFINE_TRACE(HTMLSlotElement)
 {
     visitor->trace(m_assignedNodes);
     visitor->trace(m_distributedNodes);
+    visitor->trace(m_oldDistributedNodes);
     visitor->trace(m_distributedIndices);
     HTMLElement::trace(visitor);
 }
 
 } // namespace blink