StyleResolverParentPusher can decide if it needs to push at creation time

Source/core/dom/Element.cpp

Index: Source/core/dom/Element.cpp
diff --git a/Source/core/dom/Element.cpp b/Source/core/dom/Element.cpp
index ff152e2f58e6c21293336eb34a94c2193d6759e3..9b2182f2e561dd2aeaac7b5d9fc340d4eb9439c5 100644
--- a/Source/core/dom/Element.cpp
+++ b/Source/core/dom/Element.cpp
@@ -109,30 +109,20 @@ using namespace XMLNames;
 
 class StyleResolverParentPusher {
 public:
-    explicit StyleResolverParentPusher(Element& parent)
+    explicit StyleResolverParentPusher(Element& parent, StyleRecalcChange change = NoChange)
         : m_parent(parent)
         , m_pushedStyleResolver(0)
     {
+        if ((change >= Inherit || parent.childNeedsStyleRecalc()) && (parent.hasChildNodes() || parent.youngestShadowRoot())) {
+            m_pushedStyleResolver = m_parent.document().styleResolver();
+            m_pushedStyleResolver->pushParentElement(m_parent);
+        }
     }
-    void push()
-    {
-        if (m_pushedStyleResolver)
-            return;
-        m_pushedStyleResolver = m_parent.document().styleResolver();
-        m_pushedStyleResolver->pushParentElement(m_parent);
-    }
+
     ~StyleResolverParentPusher()
     {
-
         if (!m_pushedStyleResolver)
             return;
-
-        // This tells us that our pushed style selector is in a bad state,
-        // so we should just bail out in that scenario.
-        ASSERT(m_pushedStyleResolver == m_parent.document().styleResolver());
-        if (m_pushedStyleResolver != m_parent.document().styleResolver())
-            return;
-
         m_pushedStyleResolver->popParentElement(m_parent);
     }
 
@@ -1366,8 +1356,6 @@ void Element::attach(const AttachContext& context)
 {
     ASSERT(document().inStyleRecalc());
 
-    StyleResolverParentPusher parentPusher(*this);
-
     // We've already been through detach when doing a lazyAttach, but we might
     // need to clear any state that's been added since then.
     if (hasRareData() && styleChangeType() == NeedsReattachStyleChange) {
@@ -1383,14 +1371,13 @@ void Element::attach(const AttachContext& context)
     if (RenderStyle* style = renderStyle())
         updateCallbackSelectors(0, style);
 
+    StyleResolverParentPusher pushParent(*this);
+
     createPseudoElementIfNeeded(BEFORE);
 
     // When a shadow root exists, it does the work of attaching the children.
-    if (ElementShadow* shadow = this->shadow()) {
-        parentPusher.push();
+    if (ElementShadow* shadow = this->shadow())
         shadow->attach(context);
-    } else if (firstChild())
-        parentPusher.push();
 
     ContainerNode::attach(context);
 
@@ -1599,13 +1586,11 @@ void Element::recalcChildStyle(StyleRecalcChange change)
     ASSERT(change >= Inherit || childNeedsStyleRecalc());
     ASSERT(!needsStyleRecalc());
 
-    StyleResolverParentPusher parentPusher(*this);
+    StyleResolverParentPusher pushParent(*this, change);
 
     for (ShadowRoot* root = youngestShadowRoot(); root; root = root->olderShadowRoot()) {
-        if (shouldRecalcStyle(change, root)) {
-            parentPusher.push();
+        if (shouldRecalcStyle(change, root))
             root->recalcStyle(change);
-        }
     }
 
     if (shouldRecalcStyle(change, this))
@@ -1624,12 +1609,10 @@ void Element::recalcChildStyle(StyleRecalcChange change)
             toText(child)->recalcTextStyle(change);
         } else if (child->isElementNode()) {
             Element* element = toElement(child);
-            if (shouldRecalcStyle(change, element)) {
-                parentPusher.push();
+            if (shouldRecalcStyle(change, element))
                 element->recalcStyle(change);
-            } else if (element->supportsStyleSharing()) {
+            else if (element->supportsStyleSharing())
                 styleResolver.addToStyleSharingList(*element);
-            }
         }
     }