# File lib/active_support/callbacks.rb, line 521
      def reset_callbacks(symbol)
        callbacks = send("_#{symbol}_callbacks")

        ActiveSupport::DescendantsTracker.descendants(self).each do |target|
          chain = target.send("_#{symbol}_callbacks")
          callbacks.each { |c| chain.delete(c) }
          target.__define_runner(symbol)
        end

        callbacks.clear
        __define_runner(symbol)
      end