@metajack 
There are 2 resons for making "build_display_list_wrapper"
1. To avoid code duplication
The code below is used both block and float function.
I think it is same code. Just purpose of refactoring.
``````````
// add box that starts block context
        for box_ in self.box_.iter() {
            box_.build_display_list(builder, dirty, offset, flow, list)
        }
````````````

2. Add custom display item for list marker. 
- To represent display list marker, we had needed a list item. I think that normal list item affects box dimension calculation. but as I checked Firefox& Chrome, list marker does not belong to its box. It was just a independent representation item and acts independently. So I had added custom list maker there for avoiding any influence to box calculation.

It it is not proper to design of servo, please let me know.
I'll follow your advice.