LibHTML: Anonymous blocks *should* inherit some properties

Okay, I got that a bit wrong. Here's what CSS 2.1 says:

"The properties of anonymous boxes are inherited from the enclosing
non-anonymous box. Non-inherited properties have their initial value."

This patch implements a better behavior by only copying the inherited
properties from the parent style.

Libraries/LibHTML/Layout/LayoutBlock.h

@@ -27,6 +27,8 @@ public:
 private:
     virtual bool is_block() const override { return true; }
 
+    NonnullRefPtr<StyleProperties> style_for_anonymous_block() const;
+
     void layout_inline_children();
     void layout_block_children();