LibHTML: Add LayoutNodeWithStyle class, make LayoutText style-less

Since LayoutText always inherits style, it shouldn't store any style of
its own. This patch adds a LayoutNodeWithStyle class to sit between
LayoutNode and everyone who wants to inherit from LayoutNode except
LayoutText :^)

Since LayoutText can never have children, we also know that the parent
of any LayoutNode is always going to be a LayoutNodeWithStyle.
So this patch makes LayoutNode::parent() return LayoutNodeWithStyle*.

Libraries/LibHTML/Layout/LayoutBlock.cpp

@@ -5,7 +5,7 @@
 #include <LibHTML/Layout/LayoutInline.h>
 
 LayoutBlock::LayoutBlock(const Node* node, NonnullRefPtr<StyleProperties> style)
-    : LayoutNode(node, move(style))
+    : LayoutNodeWithStyle(node, move(style))
 {
 }
 

Libraries/LibHTML/Layout/LayoutBlock.h

@@ -5,7 +5,7 @@
 
 class Element;
 
-class LayoutBlock : public LayoutNode {
+class LayoutBlock : public LayoutNodeWithStyle {
 public:
     LayoutBlock(const Node*, NonnullRefPtr<StyleProperties>);
     virtual ~LayoutBlock() override;

Libraries/LibHTML/Layout/LayoutInline.cpp

@@ -3,7 +3,7 @@
 #include <LibHTML/Layout/LayoutInline.h>
 
 LayoutInline::LayoutInline(const Element& element, NonnullRefPtr<StyleProperties> style)
-    : LayoutNode(&element, move(style))
+    : LayoutNodeWithStyle(&element, move(style))
 {
     set_inline(true);
 }

Libraries/LibHTML/Layout/LayoutInline.h

@@ -4,7 +4,7 @@
 
 class LayoutBlock;
 
-class LayoutInline : public LayoutNode {
+class LayoutInline : public LayoutNodeWithStyle {
 public:
     LayoutInline(const Element&, NonnullRefPtr<StyleProperties>);
     virtual ~LayoutInline() override;

Libraries/LibHTML/Layout/LayoutNode.cpp

@@ -7,9 +7,8 @@
 //#define DRAW_BOXES_AROUND_LAYOUT_NODES
 //#define DRAW_BOXES_AROUND_HOVERED_NODES
 
-LayoutNode::LayoutNode(const Node* node, RefPtr<StyleProperties> style)
+LayoutNode::LayoutNode(const Node* node)
     : m_node(node)
-    , m_style(move(style))
 {
     if (m_node)
         m_node->set_layout_node({}, this);

Libraries/LibHTML/Layout/LayoutNode.h

@@ -12,6 +12,7 @@ class Document;
 class Element;
 class LayoutBlock;
 class LayoutNode;
+class LayoutNodeWithStyle;
 class LineBoxFragment;
 class Node;
 
@@ -66,12 +67,9 @@ public:
 
     virtual LayoutNode& inline_wrapper() { return *this; }
 
-    const StyleProperties& style() const
+    const StyleProperties& style() const;
-    {
+
-        if (m_style)
+    const LayoutNodeWithStyle* parent() const;
-            return *m_style;
-        return parent()->style();
-    }
 
     void inserted_into(LayoutNode&) {}
     void removed_from(LayoutNode&) {}
@@ -79,13 +77,45 @@ public:
     virtual void split_into_lines(LayoutBlock& container);
 
 protected:
-    explicit LayoutNode(const Node*, RefPtr<StyleProperties>);
+    explicit LayoutNode(const Node*);
 
 private:
+    friend class LayoutNodeWithStyle;
+
     const Node* m_node { nullptr };
 
-    RefPtr<StyleProperties> m_style;
     BoxModelMetrics m_box_metrics;
     Rect m_rect;
     bool m_inline { false };
+    bool m_has_style { false };
 };
+
+class LayoutNodeWithStyle : public LayoutNode {
+public:
+    virtual ~LayoutNodeWithStyle() override {}
+
+    const StyleProperties& style() const { return m_style; }
+
+protected:
+    explicit LayoutNodeWithStyle(const Node* node, NonnullRefPtr<StyleProperties> style)
+        : LayoutNode(node)
+        , m_style(move(style))
+    {
+        m_has_style = true;
+    }
+
+private:
+    NonnullRefPtr<StyleProperties> m_style;
+};
+
+inline const StyleProperties& LayoutNode::style() const
+{
+    if (m_has_style)
+        return static_cast<const LayoutNodeWithStyle*>(this)->style();
+    return parent()->style();
+}
+
+inline const LayoutNodeWithStyle* LayoutNode::parent() const
+{
+    return static_cast<const LayoutNodeWithStyle*>(TreeNode<LayoutNode>::parent());
+}

Libraries/LibHTML/Layout/LayoutReplaced.cpp

@@ -3,7 +3,7 @@
 #include <LibHTML/Layout/LayoutReplaced.h>
 
 LayoutReplaced::LayoutReplaced(const Element& element, NonnullRefPtr<StyleProperties> style)
-    : LayoutNode(&element, move(style))
+    : LayoutNodeWithStyle(&element, move(style))
 {
     // FIXME: Allow non-inline replaced elements.
     set_inline(true);

Libraries/LibHTML/Layout/LayoutReplaced.h

@@ -1,7 +1,7 @@
 #include <LibHTML/DOM/Element.h>
 #include <LibHTML/Layout/LayoutNode.h>
 
-class LayoutReplaced : public LayoutNode {
+class LayoutReplaced : public LayoutNodeWithStyle {
 public:
     LayoutReplaced(const Element&, NonnullRefPtr<StyleProperties>);
     virtual ~LayoutReplaced() override;

Libraries/LibHTML/Layout/LayoutText.cpp

@@ -8,7 +8,7 @@
 #include <ctype.h>
 
 LayoutText::LayoutText(const Text& text)
-    : LayoutNode(&text, {})
+    : LayoutNode(&text)
 {
     set_inline(true);
 }