Move config.default_asset_host_protocol to the railtie.

actionpack/lib/sprockets/helpers/rails_helper.rb

@@ -9,13 +9,8 @@ module Sprockets
       def asset_paths
         @asset_paths ||= begin
           config     = self.config if respond_to?(:config)
+          config   ||= Rails.application.config
           controller = self.controller if respond_to?(:controller)
-          config ||= Rails.application.config
-          if config.action_controller.present?
-            config.action_controller.default_asset_host_protocol ||= :relative
-          else
-            config.default_asset_host_protocol ||= :relative
-          end
           paths = RailsHelper::AssetPaths.new(config, controller)
           paths.asset_environment = asset_environment
           paths.asset_prefix      = asset_prefix

actionpack/lib/sprockets/railtie.rb

@@ -5,6 +5,8 @@ module Sprockets
 
   # TODO: Get rid of config.assets.enabled
   class Railtie < ::Rails::Railtie
+    config.default_asset_host_protocol = :relative
+
     rake_tasks do
       load "sprockets/assets.rake"
     end