Use AS::Concern in ActiveModel

activemodel/lib/active_model/validations.rb

 module ActiveModel
   module Validations
-    def self.included(base) # :nodoc:
-      base.extend(ClassMethods)
-      base.__send__(:include, ActiveSupport::Callbacks)
-      base.define_callbacks :validate
+    extend ActiveSupport::Concern
+    include ActiveSupport::Callbacks
+
+    included do
+      define_callbacks :validate
     end
 
     module ClassMethods

activemodel/lib/active_model/validations_repair_helper.rb

 module ActiveModel
   module ValidationsRepairHelper
-    def self.included(base)
-      base.class_eval do
-        extend ClassMethods
-      end
-    end
+    extend ActiveSupport::Concern
 
     module Toolbox
       def self.record_validations(*model_classes)