Libraries: Create top level directory for libraries.

Things were getting a little crowded in the project root, so this patch
moves the Lib*/ directories into Libraries/.

Libraries/LibHTML/CSS/StyleValue.h

@@ -0,0 +1,70 @@
+#pragma once
+
+#include <AK/AKString.h>
+#include <AK/RefCounted.h>
+#include <AK/RefPtr.h>
+#include <AK/StringView.h>
+#include <LibHTML/CSS/Length.h>
+
+class StyleValue : public RefCounted<StyleValue> {
+public:
+    virtual ~StyleValue();
+
+    enum class Type {
+        Invalid,
+        Inherit,
+        Initial,
+        String,
+        Length,
+    };
+
+    Type type() const { return m_type; }
+
+    virtual String to_string() const = 0;
+
+protected:
+    explicit StyleValue(Type);
+
+private:
+    Type m_type { Type::Invalid };
+};
+
+class StringStyleValue : public StyleValue {
+public:
+    static NonnullRefPtr<StringStyleValue> create(const String& string)
+    {
+        return adopt(*new StringStyleValue(string));
+    }
+    virtual ~StringStyleValue() override {}
+
+    String to_string() const override { return m_string; }
+
+private:
+    explicit StringStyleValue(const String& string)
+        : StyleValue(Type::String)
+        , m_string(string)
+    {
+    }
+
+    String m_string;
+};
+
+class LengthStyleValue : public StyleValue {
+public:
+    static NonnullRefPtr<LengthStyleValue> create(const Length& length)
+    {
+        return adopt(*new LengthStyleValue(length));
+    }
+    virtual ~LengthStyleValue() override {}
+
+    String to_string() const override { return m_length.to_string(); }
+
+private:
+    explicit LengthStyleValue(const Length& length)
+        : StyleValue(Type::Length)
+        , m_length(length)
+    {
+    }
+
+    Length m_length;
+};