Improve RAII of StyleResolverState.

Source/core/css/resolver/ElementResolveContext.cpp

 /*
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 14 matching lines @@
 #include "core/dom/Node.h"
 #include "core/dom/NodeRenderStyle.h"
 #include "core/dom/NodeRenderingTraversal.h"
 #include "core/dom/VisitedLinkState.h"
 
 namespace blink {
 
 ElementResolveContext::ElementResolveContext(const Document& document)
     : m_element(nullptr)
     , m_parentNode(nullptr)
+    , m_parentStyle(nullptr)
     , m_rootElementStyle(document.documentElement() ? document.documentElement()->renderStyle() : document.renderStyle())
     , m_elementLinkState(NotInsideLink)
     , m_distributedToInsertionPoint(false)
 {
 }
 
-ElementResolveContext::ElementResolveContext(Element& element)
+ElementResolveContext::ElementResolveContext(Element& element, RenderStyle* parentStyle)
     : m_element(&element)
+    , m_parentStyle(parentStyle)
     , m_elementLinkState(element.document().visitedLinkState().determineLinkState(element))
     , m_distributedToInsertionPoint(false)
 {
     NodeRenderingTraversal::ParentDetails parentDetails;
     m_parentNode = NodeRenderingTraversal::parent(&element, &parentDetails);
     m_distributedToInsertionPoint = parentDetails.insertionPoint();
 
     const Document& document = element.document();
     Node* documentElement = document.documentElement();
     RenderStyle* documentStyle = document.renderStyle();
     m_rootElementStyle = documentElement && element != documentElement ? documentElement->renderStyle() : documentStyle;
     if (!m_rootElementStyle)
         m_rootElementStyle = documentStyle;
+    if (!m_parentStyle && m_parentNode)
+        m_parentStyle = m_parentNode->renderStyle();
 }
 
 } // namespace blink