Partly revert 1e526788e6

Some attr_readers should be `protected` instead of `private`

See https://travis-ci.org/rails/rails/builds/342800276

actionpack/lib/action_dispatch/http/mime_type.rb

@@ -279,9 +279,12 @@ module Mime
 
     def all?; false; end
 
-    private
+    protected
+
       attr_reader :string, :synonyms
 
+    private
+
       def to_ary; end
       def to_a; end
 

activerecord/lib/active_record/type/adapter_specific_registry.rb

@@ -53,6 +53,9 @@ module ActiveRecord
       end
 
       protected
+
+        attr_reader :name, :block, :adapter, :override
+
         def priority
           result = 0
           if adapter
@@ -69,7 +72,6 @@ module ActiveRecord
         end
 
       private
-        attr_reader :name, :block, :adapter, :override
 
         def matches_adapter?(adapter: nil, **)
           (self.adapter.nil? || adapter == self.adapter)