Make slots in non-shadow trees participate in a flat tree

third_party/WebKit/Source/core/dom/Node.cpp

Index: third_party/WebKit/Source/core/dom/Node.cpp
diff --git a/third_party/WebKit/Source/core/dom/Node.cpp b/third_party/WebKit/Source/core/dom/Node.cpp
index bb83ec98218b18f963f7fbeec0bdc7b17702883c..0de3ef3e8fb1f9c489a3aaafc0cbd78717d2d243 100644
--- a/third_party/WebKit/Source/core/dom/Node.cpp
+++ b/third_party/WebKit/Source/core/dom/Node.cpp
@@ -993,11 +993,13 @@ bool Node::isStyledElement() const {
 
 bool Node::canParticipateInFlatTree() const {
   // TODO(hayato): Return false for pseudo elements.
-  return !isShadowRoot() && !isSlotOrActiveInsertionPoint();
+  return !isShadowRoot() && !isActiveSlotOrActiveInsertionPoint();
 }
 
-bool Node::isSlotOrActiveInsertionPoint() const {
-  return isHTMLSlotElement(*this) || isActiveInsertionPoint(*this);
+bool Node::isActiveSlotOrActiveInsertionPoint() const {
+  return (isHTMLSlotElement(*this) &&
+          toHTMLSlotElement(*this).supportsDistribution()) ||
+         isActiveInsertionPoint(*this);
 }
 
 AtomicString Node::slotName() const {