Defer pushing the parent stack in recalcStyle until StyleResolver::styleForElement()

Source/core/css/resolver/StyleResolverParentScope.h

Index: Source/core/css/resolver/StyleResolverParentScope.h
diff --git a/Source/core/css/resolver/StyleResolverParentScope.h b/Source/core/css/resolver/StyleResolverParentScope.h
new file mode 100644
index 0000000000000000000000000000000000000000..58624fa2b83269747e2cdc72de92f9a1b22832ed
--- /dev/null
+++ b/Source/core/css/resolver/StyleResolverParentScope.h
@@ -0,0 +1,65 @@
+// Copyright 2014 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef StyleResolverParentScope_h
+#define StyleResolverParentScope_h
+
+#include "core/css/resolver/StyleResolver.h"
+#include "core/dom/Element.h"
+
+namespace WebCore {
+
+// Maintains the parent element stack (and bloom filter) inside recalcStyle.
+class StyleResolverParentScope FINAL {
+public:
+    explicit StyleResolverParentScope(Element& parent);
+    ~StyleResolverParentScope();
+
+    static void ensureParentStackIsPushed();
+
+private:
+    void pushParentIfNeeded();
+
+    Element& m_parent;
+    bool m_pushed;
+    StyleResolverParentScope* m_previous;
+
+    static StyleResolverParentScope* s_currentScope;
+};
+
+inline StyleResolverParentScope::StyleResolverParentScope(Element& parent)
+    : m_parent(parent)
+    , m_pushed(false)
+    , m_previous(s_currentScope)
+{
+    ASSERT(m_parent.document().inStyleRecalc());
+    s_currentScope = this;
+}
+
+inline StyleResolverParentScope::~StyleResolverParentScope()
+{
+    if (m_pushed)
+        m_parent.document().styleResolver()->popParentElement(m_parent);
+    s_currentScope = m_previous;
+}
+
+inline void StyleResolverParentScope::ensureParentStackIsPushed()
+{
+    if (s_currentScope)
+        s_currentScope->pushParentIfNeeded();
+}
+
+inline void StyleResolverParentScope::pushParentIfNeeded()
+{
+    if (m_pushed)
+        return;
+    if (m_previous)
+        m_previous->pushParentIfNeeded();
+    m_parent.document().styleResolver()->pushParentElement(m_parent);
+    m_pushed = true;
+}
+
+} // namespace WebCore
+
+#endif // StyleResolverParentScope_h