Moves application helper logic for system header and footer to its EE counterpart

app/helpers/application_helper.rb

@@ -283,23 +283,10 @@ module ApplicationHelper
     end
   end
 
-  def appearance
-    @appearance ||= Appearance.current
-  end
-
   def page_class
     class_names = []
     class_names << 'issue-boards-page' if current_controller?(:boards)
     class_names << 'with-performance-bar' if performance_bar_enabled?
-    class_names += system_message_class
-
-    class_names
-  end
-
-  def system_message_class
-    class_names = []
-    class_names << 'with-system-header' if appearance.show_header?
-    class_names << 'with-system-footer' if appearance.show_footer?
 
     class_names
   end

ee/app/helpers/ee/application_helper.rb

@@ -9,5 +9,29 @@ module EE
       (_('You are on a secondary (read-only) Geo node. If you want to make any changes, you must visit the %{primary_node}.') %
         { primary_node: link_to('primary node', ::Gitlab::Geo.primary_node.url) }).html_safe
     end
+
+    def page_class
+      class_names = super
+      class_names += system_message_class
+
+      class_names
+    end
+
+    def system_message_class
+      class_names = []
+
+      return class_names unless appearance
+
+      class_names << 'with-system-header' if appearance.show_header?
+      class_names << 'with-system-footer' if appearance.show_footer?
+
+      class_names
+    end
+
+    private
+
+    def appearance
+      ::Appearance.current
+    end
   end
 end