LibHTML: Start fleshing out block layout.

The basic idea of block layout is: width, then children based on width,
then height based on height of children.

LibHTML/Layout/LayoutBlock.cpp

@@ -12,7 +12,19 @@ LayoutBlock::~LayoutBlock()
 
 void LayoutBlock::layout()
 {
+    compute_width();
+
     LayoutNode::layout();
 
+    compute_height();
+}
+
+void LayoutBlock::compute_width()
+{
+
+}
+
+void LayoutBlock::compute_height()
+{
 
 }

LibHTML/Layout/LayoutBlock.h

@@ -14,4 +14,8 @@ public:
     virtual void layout() override;
 
 private:
+    virtual bool is_block() const override { return true; }
+
+    void compute_width();
+    void compute_height();
 };

LibHTML/Layout/LayoutDocument.h

@@ -1,9 +1,9 @@
 #pragma once
 
-#include <LibHTML/Layout/LayoutNode.h>
+#include <LibHTML/Layout/LayoutBlock.h>
 #include <LibHTML/DOM/Document.h>
 
-class LayoutDocument final : public LayoutNode {
+class LayoutDocument final : public LayoutBlock {
 public:
     explicit LayoutDocument(const Document&);
     virtual ~LayoutDocument() override;

LibHTML/Layout/LayoutNode.cpp

@@ -1,3 +1,4 @@
+#include <LibHTML/Layout/LayoutBlock.h>
 #include <LibHTML/Layout/LayoutNode.h>
 
 LayoutNode::LayoutNode(const Node* node)
@@ -15,3 +16,12 @@ void LayoutNode::layout()
         child.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);
+    }
+    return nullptr;
+}

LibHTML/Layout/LayoutNode.h

@@ -7,6 +7,7 @@
 #include <SharedGraphics/Rect.h>
 
 class Node;
+class LayoutBlock;
 
 class LayoutNode : public TreeNode<LayoutNode> {
 public:
@@ -38,9 +39,12 @@ public:
 
     virtual const char* class_name() const { return "LayoutNode"; }
     virtual bool is_text() const { return false; }
+    virtual bool is_block() const { return false; }
 
     virtual void layout();
 
+    const LayoutBlock* containing_block() const;
+
 protected:
     explicit LayoutNode(const Node*);