code: function Mixin_setInstanceKey(hostClass, method, instanceKey) {
      check(hostClass, Function);
      check(instanceKey, Match.IdentifierString);
  
      var prop = INSTANCE_PROPERTIES_MAP,
          instanceKeys = hostClass[prop] = hostClass[prop] || {};
  
      if (instanceKeys[method.name])
          throw new Error('Mixin: instance property for method with name '
              + method.name + ' is already set');
  
      instanceKeys[method.name] = instanceKey;
  }
docs: Sets mixin instance property name on the host class
  Can be called only once
  
  @private
  @param {Function} this Mixin subclass (not instance)
  @param {Function} hostClass
  @param {String} instanceKey