LibWeb: Destroy ICB formatting context before committing used values

Absolutely positioned boxes are handled by the BFC destructor, so we
need to make sure the ICB BFC is destroyed if we want these boxes
to get laid out.

Userland/Libraries/LibWeb/DOM/Document.cpp

@@ -616,17 +616,20 @@ void Document::update_layout()
 
     Layout::LayoutState layout_state;
     layout_state.used_values_per_layout_node.resize(layout_node_count());
-    Layout::BlockFormattingContext root_formatting_context(layout_state, *m_layout_root, nullptr);
 
-    auto& icb = static_cast<Layout::InitialContainingBlock&>(*m_layout_root);
-    auto& icb_state = layout_state.get_mutable(icb);
-    icb_state.set_content_width(viewport_rect.width());
-    icb_state.set_content_height(viewport_rect.height());
+    {
+        Layout::BlockFormattingContext root_formatting_context(layout_state, *m_layout_root, nullptr);
 
-    icb.set_has_definite_width(true);
-    icb.set_has_definite_height(true);
+        auto& icb = static_cast<Layout::InitialContainingBlock&>(*m_layout_root);
+        auto& icb_state = layout_state.get_mutable(icb);
+        icb.set_has_definite_width(true);
+        icb.set_has_definite_height(true);
+        icb_state.set_content_width(viewport_rect.width());
+        icb_state.set_content_height(viewport_rect.height());
+
+        root_formatting_context.run(*m_layout_root, Layout::LayoutMode::Normal);
+    }
 
-    root_formatting_context.run(*m_layout_root, Layout::LayoutMode::Normal);
     layout_state.commit();
 
     browsing_context()->set_needs_display();