LibWeb: Actually distribute free space to flex items with auto margins

We were not applying the distributed space to the used offset of flex
items, as we were only assigning the margins to the layout state of the
box, not the internal FlexItem::margins.

Userland/Libraries/LibWeb/Layout/FlexFormattingContext.cpp

@@ -412,20 +412,22 @@ void FlexFormattingContext::set_offset(Box const& box, float main_offset, float
         m_state.get_mutable(box).offset = Gfx::FloatPoint { cross_offset, main_offset };
 }
 
-void FlexFormattingContext::set_main_axis_first_margin(Box const& box, float margin)
+void FlexFormattingContext::set_main_axis_first_margin(FlexItem& item, float margin)
 {
+    item.margins.main_before = margin;
     if (is_row_layout())
-        m_state.get_mutable(box).margin_left = margin;
+        m_state.get_mutable(item.box).margin_left = margin;
     else
-        m_state.get_mutable(box).margin_top = margin;
+        m_state.get_mutable(item.box).margin_top = margin;
 }
 
-void FlexFormattingContext::set_main_axis_second_margin(Box const& box, float margin)
+void FlexFormattingContext::set_main_axis_second_margin(FlexItem& item, float margin)
 {
+    item.margins.main_after = margin;
     if (is_row_layout())
-        m_state.get_mutable(box).margin_right = margin;
+        m_state.get_mutable(item.box).margin_right = margin;
     else
-        m_state.get_mutable(box).margin_bottom = margin;
+        m_state.get_mutable(item.box).margin_bottom = margin;
 }
 
 float FlexFormattingContext::sum_of_margin_padding_border_in_main_axis(Box const& box) const
@@ -1067,16 +1069,16 @@ void FlexFormattingContext::distribute_any_remaining_free_space()
             float size_per_auto_margin = remaining_free_space / (float)auto_margins;
             for (auto& flex_item : flex_line.items) {
                 if (is_main_axis_margin_first_auto(flex_item->box))
-                    set_main_axis_first_margin(flex_item->box, size_per_auto_margin);
+                    set_main_axis_first_margin(*flex_item, size_per_auto_margin);
                 if (is_main_axis_margin_second_auto(flex_item->box))
-                    set_main_axis_second_margin(flex_item->box, size_per_auto_margin);
+                    set_main_axis_second_margin(*flex_item, size_per_auto_margin);
             }
         } else {
             for (auto& flex_item : flex_line.items) {
                 if (is_main_axis_margin_first_auto(flex_item->box))
-                    set_main_axis_first_margin(flex_item->box, 0);
+                    set_main_axis_first_margin(*flex_item, 0);
                 if (is_main_axis_margin_second_auto(flex_item->box))
-                    set_main_axis_second_margin(flex_item->box, 0);
+                    set_main_axis_second_margin(*flex_item, 0);
             }
         }
 

Userland/Libraries/LibWeb/Layout/FlexFormattingContext.h

@@ -87,8 +87,8 @@ private:
     void set_main_size(Box const&, float size);
     void set_cross_size(Box const&, float size);
     void set_offset(Box const&, float main_offset, float cross_offset);
-    void set_main_axis_first_margin(Box const&, float margin);
-    void set_main_axis_second_margin(Box const&, float margin);
+    void set_main_axis_first_margin(FlexItem&, float margin);
+    void set_main_axis_second_margin(FlexItem&, float margin);
 
     void copy_dimensions_from_flex_items_to_boxes();