Browser+LibHTML: Change the way computed styles are queried

Author: https://github.com/Matrix89
Commit: 2dd35916e5
Pull-request: https://github.com/SerenityOS/serenity/pull/1006
Reviewed-by: https://github.com/awesomekling

Libraries/LibHTML/DOM/Element.h

@@ -57,6 +57,7 @@ public:
     String name() const { return attribute("name"); }
 
     const StyleProperties* resolved_style() const { return m_resolved_style.ptr(); }
+    RefPtr<StyleProperties> computed_style();
 
 private:
     RefPtr<LayoutNode> create_layout_node(const StyleProperties* parent_style) const override;