Introduce Position::nodeAsRangeLastNode

Source/core/dom/Position.cpp

Index: Source/core/dom/Position.cpp
diff --git a/Source/core/dom/Position.cpp b/Source/core/dom/Position.cpp
index cbb1e1ed590b43906b54a9ec21e46e5ba0e69d7a..851407716b77748218f4557be5b50b7315d7e118 100644
--- a/Source/core/dom/Position.cpp
+++ b/Source/core/dom/Position.cpp
@@ -320,6 +320,16 @@ Node* PositionAlgorithm<Strategy>::nodeAsRangeFirstNode() const
     return Strategy::nextSkippingChildren(*m_anchorNode);
 }
 
+template <typename Strategy>
+Node* PositionAlgorithm<Strategy>::nodeAsRangeLastNode() const
+{
+    if (isNull())
+        return nullptr;
+    if (Node* pastLastNode = nodeAsRangePastLastNode())
+        return Strategy::previous(*pastLastNode);
+    return &Strategy::lastWithinOrSelf(*containerNode());
+}
+
 // An implementation of |Range::pastLastNode()|.
 template <typename Strategy>
 Node* PositionAlgorithm<Strategy>::nodeAsRangePastLastNode() const