LibWeb: Make DisplayList ref-counted

This change is a preparation for the upcoming changes where display
list will be nested and the same display could be owned by multiple
display list items.

Userland/Libraries/LibWeb/HTML/TraversableNavigable.cpp

@@ -1190,7 +1190,7 @@ JS::GCPtr<DOM::Node> TraversableNavigable::currently_focused_area()
 
 void TraversableNavigable::paint(DevicePixelRect const& content_rect, Painting::BackingStore& target, PaintOptions paint_options)
 {
-    Painting::DisplayList display_list;
+    auto display_list = Painting::DisplayList::create();
     Painting::DisplayListRecorder display_list_recorder(display_list);
 
     Gfx::IntRect bitmap_rect { {}, content_rect.size().to_type<int>() };

Userland/Libraries/LibWeb/Painting/DisplayList.h

@@ -73,8 +73,13 @@ private:
     virtual bool would_be_fully_clipped_by_painter(Gfx::IntRect) const = 0;
 };
 
-class DisplayList {
+class DisplayList : public RefCounted<DisplayList> {
 public:
+    static NonnullRefPtr<DisplayList> create()
+    {
+        return adopt_ref(*new DisplayList());
+    }
+
     void append(Command&& command, Optional<i32> scroll_frame_id);
 
     void apply_scroll_offsets(Vector<Gfx::IntPoint> const& offsets_by_frame_id);
@@ -89,6 +94,8 @@ public:
     AK::SegmentedVector<CommandListItem, 512> const& commands() const { return m_commands; }
 
 private:
+    DisplayList() = default;
+
     AK::SegmentedVector<CommandListItem, 512> m_commands;
 };
 

Userland/Libraries/LibWeb/Painting/SVGMaskable.cpp

@@ -81,8 +81,8 @@ RefPtr<Gfx::Bitmap> SVGMaskable::calculate_mask_of_svg(PaintContext& context, CS
         if (mask_bitmap_or_error.is_error())
             return {};
         mask_bitmap = mask_bitmap_or_error.release_value();
-        DisplayList display_list;
-        DisplayListRecorder display_list_recorder(display_list);
+        auto display_list = DisplayList::create();
+        DisplayListRecorder display_list_recorder(*display_list);
         display_list_recorder.translate(-mask_rect.location().to_type<int>());
         auto paint_context = context.clone(display_list_recorder);
         paint_context.set_svg_transform(graphics_element.get_transform());

Userland/Libraries/LibWeb/SVG/SVGDecodedImageData.cpp

@@ -92,7 +92,7 @@ RefPtr<Gfx::Bitmap> SVGDecodedImageData::render(Gfx::IntSize size) const
     m_document->navigable()->set_viewport_size(size.to_type<CSSPixels>());
     m_document->update_layout();
 
-    Painting::DisplayList display_list;
+    auto display_list = Painting::DisplayList::create();
     Painting::DisplayListRecorder display_list_recorder(display_list);
 
     m_document->navigable()->record_display_list(display_list_recorder, {});