Stop violating law of demeter in response cookie_jar

This adds a new method to request and response so we don't need to
violate the law of demeter.

We are changing `Request` and `Response` so that they always have a
`cookie_jar`

This is a continuation on work to combine integration and controller
test code bases in Rails.

actionpack/lib/action_dispatch/http/request.rb

@@ -63,6 +63,9 @@ def initialize(env)
       @ip                = nil
     end
 
+    def commit_cookie_jar! # :nodoc:
+    end
+
     def check_path_parameters!
       # If any of the path parameters has an invalid encoding then
       # raise since it's likely to trigger errors further on.

actionpack/lib/action_dispatch/http/response.rb

@@ -413,7 +413,7 @@ def before_committed
 
     def before_sending
       headers.freeze
-      request.cookie_jar.commit!
+      request.commit_cookie_jar!
     end
 
     def build_buffer(response, body)

actionpack/lib/action_dispatch/middleware/cookies.rb

@@ -12,6 +12,12 @@ def cookie_jar
     end
 
     # :stopdoc:
+    prepend Module.new {
+      def commit_cookie_jar!
+        cookie_jar.commit!
+      end
+    }
+
     def have_cookie_jar?
       has_header? 'action_dispatch.cookies'.freeze
     end