LibHTML: Add Length and LengthBox classes.

We need a way to represent values that are "auto", so adding a Length class
seems like the easiest way to achieve that.

LibHTML/CSS/Length.h

@@ -0,0 +1,26 @@
+#pragma once
+
+class Length {
+public:
+    enum class Type {
+        Auto,
+        Absolute,
+    };
+
+    Length() {}
+    Length(int value, Type type)
+        : m_type(type)
+        , m_value(value)
+    {
+    }
+    ~Length() {}
+
+    bool is_auto() const { return m_type == Type::Auto; }
+    bool is_absolute() const { return m_type == Type::Absolute; }
+
+    int value() const { return m_value; }
+
+private:
+    Type m_type { Type::Auto };
+    int m_value { 0 };
+};

LibHTML/CSS/LengthBox.h

@@ -0,0 +1,10 @@
+#pragma once
+
+#include <LibHTML/CSS/Length.h>
+
+struct LengthBox {
+    Length top;
+    Length right;
+    Length bottom;
+    Length left;
+};

LibHTML/Layout/LayoutBlock.cpp

@@ -21,10 +21,8 @@ void LayoutBlock::layout()
 
 void LayoutBlock::compute_width()
 {
-
 }
 
 void LayoutBlock::compute_height()
 {
-
 }

LibHTML/Layout/LayoutStyle.h

@@ -1,15 +1,9 @@
 #pragma once
 
+#include <LibHTML/CSS/LengthBox.h>
 #include <SharedGraphics/Color.h>
 #include <SharedGraphics/Size.h>
 
-struct Box {
-    int top { 0 };
-    int right { 0 };
-    int bottom { 0 };
-    int left { 0 };
-};
-
 enum FontStyle {
     Normal,
     Bold,
@@ -23,13 +17,15 @@ public:
     Color text_color() const { return m_text_color; }
     Color background_color() const { return m_background_color; }
 
-    Box& offset() { return m_offset; }
-    Box& margin() { return m_margin; }
-    Box& padding() { return m_padding; }
+    LengthBox& offset() { return m_offset; }
+    LengthBox& margin() { return m_margin; }
+    LengthBox& padding() { return m_padding; }
+    LengthBox& border() { return m_border; }
 
-    const Box& offset() const { return m_offset; }
-    const Box& margin() const { return m_margin; }
-    const Box& padding() const { return m_padding; }
+    const LengthBox& offset() const { return m_offset; }
+    const LengthBox& margin() const { return m_margin; }
+    const LengthBox& padding() const { return m_padding; }
+    const LengthBox& border() const { return m_border; }
 
     FontStyle font_style() const { return m_font_style; }
 
@@ -40,9 +36,10 @@ private:
     Color m_text_color;
     Color m_background_color;
 
-    Box m_offset;
-    Box m_margin;
-    Box m_padding;
+    LengthBox m_offset;
+    LengthBox m_margin;
+    LengthBox m_padding;
+    LengthBox m_border;
 
     Size m_size;