Have ScopedStyleResolver deal with ContainerNode references, not pointers

Source/core/dom/shadow/ShadowRoot.h

Index: Source/core/dom/shadow/ShadowRoot.h
diff --git a/Source/core/dom/shadow/ShadowRoot.h b/Source/core/dom/shadow/ShadowRoot.h
index c70c0e26e060cb98ab56323c864a16f3ecb933b0..1ad8bf110816836edd644b3ed5d1d0f9b5009ff7 100644
--- a/Source/core/dom/shadow/ShadowRoot.h
+++ b/Source/core/dom/shadow/ShadowRoot.h
@@ -161,6 +161,12 @@ inline ShadowRoot* toShadowRoot(Node* node)
     return const_cast<ShadowRoot*>(toShadowRoot(static_cast<const Node*>(node)));
 }
 
+inline const ShadowRoot& toShadowRoot(const Node& node)
+{
+    ASSERT_WITH_SECURITY_IMPLICATION(node.isShadowRoot());
+    return static_cast<const ShadowRoot&>(node);
+}
+
 inline const ShadowRoot* toShadowRoot(const TreeScope* treeScope)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!treeScope || (treeScope->rootNode() && treeScope->rootNode()->isShadowRoot()));