Do not allocate SlotAssignment unless a shadowroot has a slot

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

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  *           (C) 2001 Peter Kelly (pmk@post.com)
  *           (C) 2001 Dirk Mueller (mueller@kde.org)
  *           (C) 2007 David Smith (catfish.man@gmail.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2012, 2013 Apple Inc.
  * All rights reserved.
  *           (C) 2007 Eric Seidel (eric@webkit.org)
  *
@@ skipping 1272 matching lines @@
 DISABLE_CFI_PERF
 void Element::attributeChanged(const AttributeModificationParams& params) {
   const QualifiedName& name = params.name;
   if (ElementShadow* parentElementShadow =
           shadowWhereNodeCanBeDistributedForV0(*this)) {
     if (shouldInvalidateDistributionWhenAttributeChanged(parentElementShadow,
                                                          name, params.newValue))
       parentElementShadow->setNeedsDistributionRecalc();
   }
   if (name == HTMLNames::slotAttr && params.oldValue != params.newValue) {
-    if (ShadowRoot* root = v1ShadowRootOfParent()) {
-      root->ensureSlotAssignment().hostChildSlotNameChanged(params.oldValue,
-                                                            params.newValue);
-    }
+    if (ShadowRoot* root = v1ShadowRootOfParent())
+      root->didChangeHostChildSlotName(params.oldValue, params.newValue);
   }
 
   parseAttribute(params);
 
   document().incDOMTreeVersion();
 
   if (name == HTMLNames::idAttr) {
     AtomicString oldId = elementData()->idForStyleResolution();
     AtomicString newId =
         makeIdForStyleResolution(params.newValue, document().inQuirksMode());
@@ skipping 2823 matching lines @@
 }
 
 DEFINE_TRACE_WRAPPERS(Element) {
   if (hasRareData()) {
     visitor->traceWrappers(elementRareData());
   }
   ContainerNode::traceWrappers(visitor);
 }
 
 }  // namespace blink