8042778: Getting all visible methods in ReferenceTypeImpl is slow

Reviewed-by: egahlin, dholmes

jdk/src/share/classes/com/sun/tools/jdi/ReferenceTypeImpl.java

@@ -529,7 +529,7 @@ implements ReferenceType {
          * to filter that ordered collection.
          */
         List<Method> list = allMethods();
-        list.retainAll(map.values());
+        list.retainAll(new HashSet<Method>(map.values()));
         return list;
     }