Delay construction of StyleResolverState until after style sharing.

Source/core/css/resolver/StyleResolver.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/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 543 matching lines @@
         }
 
         document().setHasNodesWithPlaceholderStyle();
         return s_styleNotYetAvailable;
     }
 
     didAccess();
 
     StyleResolverParentScope::ensureParentStackIsPushed();
 
-    StyleResolverState state(document(), element, defaultParent);
+    ElementResolveContext elementContext(*element);
 
-    if (sharingBehavior == AllowStyleSharing && state.parentStyle()) {
-        SharedStyleFinder styleFinder(state.elementContext(), m_features, m_siblingRuleSet.get(), m_uncommonAttributeRuleSet.get(), *this);
+    if (sharingBehavior == AllowStyleSharing && (defaultParent || elementContext.parentStyle())) {
+        SharedStyleFinder styleFinder(elementContext, m_features, m_siblingRuleSet.get(), m_uncommonAttributeRuleSet.get(), *this);
         if (RefPtr<RenderStyle> sharedStyle = styleFinder.findSharedStyle())
             return sharedStyle.release();
     }
 
+    StyleResolverState state(document(), elementContext, defaultParent);

[andersr, 2014/12/02 14:08:17]

I ran blink_perf.css locally on this patch, and I didn't find any performance
issues related to the copying of ElementResolveContext.

If it turns out that I'm wrong, it's pretty easy to mitigate anyway by always
creating the ElementResolveContext separately, and just keeping a reference in
StyleResolverState.

+
     ActiveAnimations* activeAnimations = element->activeAnimations();
     const RenderStyle* baseRenderStyle = activeAnimations ? activeAnimations->baseRenderStyle() : nullptr;
 
     if (baseRenderStyle) {
         state.setStyle(RenderStyle::clone(baseRenderStyle));
         if (!state.parentStyle())
             state.setParentStyle(defaultStyleForElement());
     } else {
         if (state.parentStyle()) {
             RefPtr<RenderStyle> style = RenderStyle::create();
@@ skipping 1022 matching lines @@
     visitor->trace(m_uncommonAttributeRuleSet);
     visitor->trace(m_watchedSelectorsRules);
     visitor->trace(m_treeBoundaryCrossingRules);
     visitor->trace(m_styleSharingLists);
     visitor->trace(m_pendingStyleSheets);
     visitor->trace(m_document);
 #endif
 }
 
 } // namespace blink