Do not allocate SlotAssignment unless a shadowroot has a slot

third_party/WebKit/Source/core/dom/shadow/ShadowRoot.cpp

 /*
  * Copyright (C) 2011 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.
  *     * Neither the name of Google Inc. nor the names of its
@@ skipping 83 matching lines @@
   DCHECK_EQ(type(), ShadowRootType::V0);
   ensureShadowRootRareDataV0().setOlderShadowRoot(root);
 }
 
 SlotAssignment& ShadowRoot::ensureSlotAssignment() {
   if (!m_slotAssignment)
     m_slotAssignment = SlotAssignment::create(*this);
   return *m_slotAssignment;
 }
 
+HTMLSlotElement* ShadowRoot::assignedSlotFor(const Node& node) {
+  if (!m_slotAssignment)
+    return nullptr;
+  return m_slotAssignment->findSlot(node);
+}
+
+void ShadowRoot::slotAdded(HTMLSlotElement& slot) {

[esprehn, 2017/01/17 10:48:18]

DidAddSlot()

[hayato, 2017/01/19 03:13:50]

Done

+  DCHECK(isV1());
+  ensureSlotAssignment().slotAdded(slot);
+}
+
+void ShadowRoot::hostChildSlotNameChanged(const AtomicString& oldValue,

[esprehn, 2017/01/17 10:48:18]

I prefer the did naming.

::DidChangeHostChildSlotName

[hayato, 2017/01/19 03:13:50]

Done

+                                          const AtomicString& newValue) {
+  if (!m_slotAssignment)
+    return;
+  m_slotAssignment->hostChildSlotNameChanged(oldValue, newValue);
+}
+
 Node* ShadowRoot::cloneNode(bool, ExceptionState& exceptionState) {
   exceptionState.throwDOMException(NotSupportedError,
                                    "ShadowRoot nodes are not clonable.");
   return nullptr;
 }
 
 String ShadowRoot::innerHTML() const {
   return createMarkup(this, ChildrenOnly);
 }
 
@@ skipping 202 matching lines @@
       ostream << "ShadowRootType::Open";
       break;
     case ShadowRootType::Closed:
       ostream << "ShadowRootType::Closed";
       break;
   }
   return ostream;
 }
 
 }  // namespace blink