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

*** 170,176 ****
--- 170,191 ----
       */
      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;
+     }
+ 
  }