private String getTagName(ViewContext context) {
    if (context == null) {
      return "<null>";
    }
    return String.format("%s:%s", context.getInstanceName(), context.getUsername());
  }
Returns unique key for Map to store a user-local variable.
@param context ViewContext
@return Unique identifier of pair instance-user.
contrib/views/utils/src/main/java/org/apache/ambari/view/utils/UserLocal.java