Move double render check out of AbstractController.

actionpack/lib/abstract_controller/rendering.rb

@@ -41,10 +41,6 @@ def view_context
     # Mostly abstracts the fact that calling render twice is a DoubleRenderError.
     # Delegates render_to_body and sticks the result in self.response_body.
     def render(*args, &block)
-      if response_body
-        raise AbstractController::DoubleRenderError
-      end
-
       options = _normalize_options(*args, &block)
       self.response_body = render_to_body(options)
     end

actionpack/lib/action_controller/metal/rendering.rb

@@ -13,6 +13,10 @@ def process_action(*)
     end
 
     def render(*args)
+      if response_body
+        raise ::AbstractController::DoubleRenderError
+      end
+
       args << {} unless args.last.is_a?(Hash)
       super(*args)
       self.content_type ||= args.last[:_template].mime_type.to_s