code: function markDeprecated(obj, eventName, insteadStr) {
          // Mark event as deprecated - on() will emit warnings when called with this event
          if (!obj._deprecatedEvents) {
              obj._deprecatedEvents = {};
          }
          obj._deprecatedEvents[eventName] = insteadStr || true;
      }
docs: Mark a given event name as deprecated, such that on() will emit warnings when called with it.
  May be called before makeEventDispatcher(). May be called on a prototype where makeEventDispatcher()
  is called separately per instance (i.e. in the constructor). Should be called before clients have
  a chance to start calling on().
  @param {!Object} obj Event dispatcher object
  @param {string} eventName Name of deprecated event
  @param {string=} insteadStr Suggested thing to use instead