convert AcceptList to a regular class

we never use this custom array outside the mime type `parse` method.  We
can reduce the interaction to just a regular array, so we should use
that instead (IOW, there was nothing special about AcceptList so we
should remove it).

actionpack/lib/action_dispatch/http/mime_type.rb

@@ -108,51 +108,50 @@ def <=>(item)
       end
     end
 
-    class AcceptList < Array #:nodoc:
-      def assort!
-        sort!
+    class AcceptList #:nodoc:
+      def self.sort!(list)
+        list.sort!
 
-        text_xml_idx = find_item_by_name self, 'text/xml'
-        app_xml_idx = find_item_by_name self, Mime[:xml].to_s
+        text_xml_idx = find_item_by_name list, 'text/xml'
+        app_xml_idx = find_item_by_name list, Mime[:xml].to_s
 
         # Take care of the broken text/xml entry by renaming or deleting it
         if text_xml_idx && app_xml_idx
-          app_xml = self[app_xml_idx]
-          text_xml = self[text_xml_idx]
+          app_xml = list[app_xml_idx]
+          text_xml = list[text_xml_idx]
 
           app_xml.q = [text_xml.q, app_xml.q].max # set the q value to the max of the two
           if app_xml_idx > text_xml_idx  # make sure app_xml is ahead of text_xml in the list
-            self[app_xml_idx], self[text_xml_idx] = text_xml, app_xml
+            list[app_xml_idx], list[text_xml_idx] = text_xml, app_xml
             app_xml_idx, text_xml_idx = text_xml_idx, app_xml_idx
           end
-          delete_at(text_xml_idx)                 # delete text_xml from the list
+          list.delete_at(text_xml_idx)                 # delete text_xml from the list
         elsif text_xml_idx
-          self[text_xml_idx].name = Mime[:xml].to_s
+          list[text_xml_idx].name = Mime[:xml].to_s
         end
 
         # Look for more specific XML-based types and sort them ahead of app/xml
         if app_xml_idx
-          app_xml = self[app_xml_idx]
+          app_xml = list[app_xml_idx]
           idx = app_xml_idx
 
-          while idx < length
-            type = self[idx]
+          while idx < list.length
+            type = list[idx]
             break if type.q < app_xml.q
 
             if type.name.ends_with? '+xml'
-              self[app_xml_idx], self[idx] = self[idx], app_xml
+              list[app_xml_idx], list[idx] = list[idx], app_xml
               app_xml_idx = idx
             end
             idx += 1
           end
         end
 
-        map! { |i| Mime::Type.lookup(i.name) }.uniq!
-        to_a
+        list.map! { |i| Mime::Type.lookup(i.name) }.uniq!
+        list
       end
 
-      private
-      def find_item_by_name(array, name)
+      def self.find_item_by_name(array, name)
         array.index { |item| item.name == name }
       end
     end
@@ -198,7 +197,7 @@ def parse(accept_header)
           accept_header = accept_header.split(PARAMETER_SEPARATOR_REGEXP).first
           parse_trailing_star(accept_header) || [Mime::Type.lookup(accept_header)].compact
         else
-          list, index = AcceptList.new, 0
+          list, index = [], 0
           accept_header.split(',').each do |header|
             params, q = header.split(PARAMETER_SEPARATOR_REGEXP)
             if params.present?
@@ -212,7 +211,7 @@ def parse(accept_header)
               end
             end
           end
-          list.assort!
+          AcceptList.sort! list
         end
       end