Clean up code duplication of isAtShadowBoundary()

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 530c3abea4b1d0cd572573266ae7736743f01af7..a2324f3fc07fbc4a9332287bc85c4391a1053a17 100644
--- a/Source/core/dom/Element.h
+++ b/Source/core/dom/Element.h
@@ -842,6 +842,14 @@ inline bool isShadowHost(const Element* element)
     return element && element->shadow();
 }
 
+inline bool isAtShadowBoundary(const Element* element)
+{
+    if (!element)
+        return false;
+    ContainerNode* parentNode = element->parentNode();
+    return parentNode && parentNode->isShadowRoot();
+}
+
 // These macros do the same as their NODE equivalents but additionally provide a template specialization
 // for isElementOfType<>() so that the Traversal<> API works for these Element types.
 #define DEFINE_ELEMENT_TYPE_CASTS(thisType, predicate) \