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

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

Index: third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
diff --git a/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp b/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
index 2af5bde13f26900e0d8b403d1a61251b83c4332c..002d534b85d7fa6c33a3046d7f51abbcc1adc9de 100644
--- a/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
@@ -139,11 +139,18 @@ void HTMLSlotElement::appendDistributedNodesFrom(const HTMLSlotElement& other)
 
 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;
@@ -291,6 +298,18 @@ void HTMLSlotElement::updateDistributedNodesWithFallback()
     }
 }
 
+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) {
@@ -338,6 +357,7 @@ DEFINE_TRACE(HTMLSlotElement)
 {
     visitor->trace(m_assignedNodes);
     visitor->trace(m_distributedNodes);
+    visitor->trace(m_oldDistributedNodes);
     visitor->trace(m_distributedIndices);
     HTMLElement::trace(visitor);
 }