Have ScopedStyleResolver deal with ContainerNode references, not pointers

Source/core/dom/Element.h

Index: Source/core/dom/Element.h
diff --git a/Source/core/dom/Element.h b/Source/core/dom/Element.h
index 87bfbafc953d3d5d3598181af30e6ac662893794..e684735f7f2dd4ece71cc6d3bfd551b17d6890b3 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -801,6 +801,12 @@ inline const Element* toElement(const Node* node)
     return static_cast<const Element*>(node);
 }
 
+inline const Element& toElement(const Node& node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(node.isElementNode());
+    return static_cast<const Element&>(node);
+}
+
 // This will catch anyone doing an unnecessary cast.
 void toElement(const Element*);