Fix FlatTreeTraversal for a slot in a document tree

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 2d4113e136e7c9ab5a5cdfb8ad5d75d4a3e4d083..580e3147f1487f36f1d5e94c1115651970a141ac 100644
--- a/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
+++ b/third_party/WebKit/Source/core/html/HTMLSlotElement.cpp
@@ -72,11 +72,8 @@ const HeapVector<Member<Node>> HTMLSlotElement::assignedNodesForBinding(
   return m_assignedNodes;
 }
 
-const HeapVector<Member<Node>>& HTMLSlotElement::getDistributedNodes() {
-  DCHECK(!needsDistributionRecalc());
-  if (isInShadowTree())
-    return m_distributedNodes;
-
+void HTMLSlotElement::updateDistributedNodesInDocumentTree() {
+  DCHECK(isInDocumentTree());
   // 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
@@ -96,6 +93,13 @@ const HeapVector<Member<Node>>& HTMLSlotElement::getDistributedNodes() {
       child = NodeTraversal::nextSkippingChildren(*child, this);
     }
   }
+}
+
+const HeapVector<Member<Node>>& HTMLSlotElement::getDistributedNodes() {
+  DCHECK(!needsDistributionRecalc());
+  // TODO(hayato): Support a disconnected node tree.
+  if (isInDocumentTree())
+    updateDistributedNodesInDocumentTree();
   return m_distributedNodes;
 }