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

Source/core/css/resolver/StyleResolverParentScope.cpp

 // 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.
 
 #include "config.h"
-#include "core/css/Pair.h"
+
+#include "core/css/resolver/StyleResolverParentScope.h"
 
 namespace WebCore {
 
-void Pair::trace(Visitor* visitor)
-{
-    visitor->trace(m_first);
-    visitor->trace(m_second);
-}
+StyleResolverParentScope* StyleResolverParentScope::s_currentScope = 0;
 
-}
+} // namespace WebCore