LibHTML: Implement rendering

Author: https://github.com/bugaevc
Commit: 235dee8c42
Pull-request: https://github.com/SerenityOS/serenity/pull/609
Reviewed-by: https://github.com/awesomekling ✅

Libraries/LibHTML/Layout/LayoutBlock.h

@@ -12,6 +12,7 @@ public:
     virtual const char* class_name() const override { return "LayoutBlock"; }
 
     virtual void layout() override;
+    virtual void render(RenderingContext&) override;
 
     virtual LayoutNode& inline_wrapper() override;