src/jdk/nashorn/internal/runtime/FindProperty.java

@@ -170,7 +170,22 @@
      */
     public void setObjectValue(final Object value, final boolean strict) {
         property.setObjectValue(getSetterReceiver(), getOwner(), value, strict);
     }
 
+    /**
+     * Get the number of objects in the prototype chain between the {@code self} and the
+     * {@code owner} objects.
+     * @return the prototype chain length
+     */
+    int getProtoChainLength() {
+        assert self != null;
+        int length = 0;
+        for (ScriptObject obj = self; obj != prototype; obj = obj.getProto()) {
+            assert !(obj instanceof WithObject);
+            ++length;
+        }
+        return length;
+    }
+
 }