Delay construction of StyleResolverState until after style sharing.

Source/core/css/resolver/StyleResolver.cpp

Index: Source/core/css/resolver/StyleResolver.cpp
diff --git a/Source/core/css/resolver/StyleResolver.cpp b/Source/core/css/resolver/StyleResolver.cpp
index e1db3dd6d754f30ebefbfdfc04b2668486223516..1d39ce659c8397fab8cfaae8213e400f299e4443 100644
--- a/Source/core/css/resolver/StyleResolver.cpp
+++ b/Source/core/css/resolver/StyleResolver.cpp
@@ -561,14 +561,16 @@ PassRefPtr<RenderStyle> StyleResolver::styleForElement(Element* element, RenderS
 
     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;