LibHTML: Add is<T> and to<T> helpers for LayoutNode class family

Libraries/LibHTML/Layout/LayoutBlock.h

@@ -53,3 +53,9 @@ void LayoutNode::for_each_fragment_of_this(Callback callback)
         }
     }
 }
+
+template<>
+inline bool is<LayoutBlock>(const LayoutNode& node)
+{
+    return node.is_block();
+}

Libraries/LibHTML/Layout/LayoutNode.cpp

@@ -31,8 +31,8 @@ void LayoutNode::layout()
 const LayoutBlock* LayoutNode::containing_block() const
 {
     for (auto* ancestor = parent(); ancestor; ancestor = ancestor->parent()) {
-        if (ancestor->is_block())
-            return static_cast<const LayoutBlock*>(ancestor);
+        if (is<LayoutBlock>(*ancestor))
+            return to<LayoutBlock>(ancestor);
     }
     return nullptr;
 }

Libraries/LibHTML/Layout/LayoutNode.h

@@ -63,6 +63,7 @@ public:
     virtual bool is_text() const { return false; }
     virtual bool is_block() const { return false; }
     virtual bool is_replaced() const { return false; }
+    bool has_style() const { return m_has_style; }
 
     bool is_inline() const { return m_inline; }
     void set_inline(bool b) { m_inline = b; }
@@ -136,3 +137,55 @@ inline const LayoutNodeWithStyle* LayoutNode::parent() const
 {
     return static_cast<const LayoutNodeWithStyle*>(TreeNode<LayoutNode>::parent());
 }
+
+template<typename T>
+inline bool is(const LayoutNode&)
+{
+    return false;
+}
+
+template<typename T>
+inline bool is(const LayoutNode* node)
+{
+    return node && is<T>(*node);
+}
+
+template<>
+inline bool is<LayoutNode>(const LayoutNode&)
+{
+    return true;
+}
+
+template<>
+inline bool is<LayoutNodeWithStyle>(const LayoutNode& node)
+{
+    return node.has_style();
+}
+
+template<typename T>
+inline const T& to(const LayoutNode& node)
+{
+    ASSERT(is<T>(node));
+    return static_cast<const T&>(node);
+}
+
+template<typename T>
+inline T* to(LayoutNode* node)
+{
+    ASSERT(is<T>(node));
+    return static_cast<T*>(node);
+}
+
+template<typename T>
+inline const T* to(const LayoutNode* node)
+{
+    ASSERT(is<T>(node));
+    return static_cast<const T*>(node);
+}
+
+template<typename T>
+inline T& to(LayoutNode& node)
+{
+    ASSERT(is<T>(node));
+    return static_cast<T&>(node);
+}

Libraries/LibHTML/Layout/LayoutReplaced.h

@@ -15,3 +15,9 @@ private:
 
     virtual void split_into_lines(LayoutBlock& container) override;
 };
+
+template<>
+inline bool is<LayoutReplaced>(const LayoutNode& node)
+{
+    return node.is_replaced();
+}

Libraries/LibHTML/Layout/LayoutText.h

@@ -31,3 +31,9 @@ private:
 
     String m_text_for_rendering;
 };
+
+template<>
+inline bool is<LayoutText>(const LayoutNode& node)
+{
+    return node.is_text();
+}

Libraries/LibHTML/Layout/LineBoxFragment.cpp

@@ -10,8 +10,7 @@ void LineBoxFragment::render(RenderingContext& context)
             return;
     }
 
-    if (layout_node().is_text()) {
-        auto& layout_text = static_cast<const LayoutText&>(layout_node());
-        layout_text.render_fragment(context, *this);
+    if (is<LayoutText>(layout_node())) {
+        to<LayoutText>(layout_node()).render_fragment(context, *this);
     }
 }