Improve RAII of StyleResolverState.

Source/core/css/resolver/ElementResolveContext.cpp

Index: Source/core/css/resolver/ElementResolveContext.cpp
diff --git a/Source/core/css/resolver/ElementResolveContext.cpp b/Source/core/css/resolver/ElementResolveContext.cpp
index 40008283689d0ecd3035fb2dba264d1b7621c678..51a86a37a10c6aee5e893481eac3771033f877b5 100644
--- a/Source/core/css/resolver/ElementResolveContext.cpp
+++ b/Source/core/css/resolver/ElementResolveContext.cpp
@@ -32,14 +32,16 @@ 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)
 {
@@ -53,6 +55,8 @@ ElementResolveContext::ElementResolveContext(Element& element)
     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