Support Style Sharing for Shadow DOM V1

third_party/WebKit/Source/core/css/resolver/SharedStyleFinder.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc.
  * All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved.
  * (http://www.torchmobile.com/)
@@ skipping 180 matching lines @@
 
   if (!elementShadow && !candidateShadow)
     return true;
 
   if (static_cast<bool>(elementShadow) != static_cast<bool>(candidateShadow))
     return false;
 
   return elementShadow->hasSameStyles(*candidateShadow);
 }
 
+bool SharedStyleFinder::sharingCandidateAssignedToSameSlot(
+    Element& candidate) const {
+  HTMLSlotElement* slot1 = element().assignedSlot();
+  HTMLSlotElement* slot2 = candidate.assignedSlot();
+  return slot1 && slot2 && slot1 == slot2;

[rune, 2017/01/11 11:34:27]

The most common case is that slot1 and slot2 are both null. Won't this skip
style sharing for the common case?

+}
+
 bool SharedStyleFinder::sharingCandidateDistributedToSameInsertionPoint(
     Element& candidate) const {
   HeapVector<Member<InsertionPoint>, 8> insertionPoints,
       candidateInsertionPoints;
   collectDestinationInsertionPoints(element(), insertionPoints);
   collectDestinationInsertionPoints(candidate, candidateInsertionPoints);
   if (insertionPoints.size() != candidateInsertionPoints.size())
     return false;
   for (size_t i = 0; i < insertionPoints.size(); ++i) {
     if (insertionPoints[i] != candidateInsertionPoints[i])
@@ skipping 33 matching lines @@
   if (!sharingCandidateHasIdenticalStyleAffectingAttributes(candidate))
     return false;
   if (candidate.additionalPresentationAttributeStyle() !=
       element().additionalPresentationAttributeStyle())
     return false;
   if (candidate.hasID() &&
       m_features.hasSelectorForId(candidate.idForStyleResolution()))
     return false;
   if (!sharingCandidateCanShareHostStyles(candidate))
     return false;
+  // For Shadow DOM V1
+  if (!sharingCandidateAssignedToSameSlot(candidate))
+    return false;
+  // For Shadow DOM V0
   if (!sharingCandidateDistributedToSameInsertionPoint(candidate))
     return false;
   if (candidate.isInTopLayer() != element().isInTopLayer())
     return false;
 
   bool isControl = candidate.isFormControlElement();
   ASSERT(isControl == element().isFormControlElement());
   if (isControl && !canShareStyleWithControl(candidate))
     return false;
 
@@ skipping 120 matching lines @@
   if (!element().parentElementOrShadowRoot()->childrenSupportStyleSharing()) {
     INCREMENT_STYLE_STATS_COUNTER(document().styleEngine(),
                                   sharedStyleRejectedByParent, 1);
     return nullptr;
   }
 
   return shareElement->mutableComputedStyle();
 }
 
 }  // namespace blink