LibWeb: Add CSSRuleList

"The CSSRuleList interface represents an ordered collection of CSS style
rules." - https://www.w3.org/TR/cssom-1/#the-cssrulelist-interface

Userland/Libraries/LibWeb/CSS/CSSRuleList.h

@@ -0,0 +1,44 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Iterator.h>
+#include <AK/NonnullRefPtrVector.h>
+#include <AK/RefCounted.h>
+#include <AK/RefPtr.h>
+#include <LibWeb/CSS/CSSRule.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::CSS {
+
+class CSSRuleList {
+public:
+    explicit CSSRuleList(NonnullRefPtrVector<CSSRule>&&);
+    virtual ~CSSRuleList();
+
+    RefPtr<CSSRule> item(size_t index) const
+    {
+        if (index >= length())
+            return nullptr;
+        return m_rules[index];
+    }
+    size_t length() const { return m_rules.size(); }
+
+    using ConstIterator = AK::SimpleIterator<AK::NonnullPtrVector<NonnullRefPtr<CSSRule>> const, CSSRule const>;
+    using Iterator = AK::SimpleIterator<AK::NonnullPtrVector<NonnullRefPtr<CSSRule>>, CSSRule>;
+
+    ConstIterator const begin() const { return m_rules.begin(); }
+    Iterator begin() { return m_rules.begin(); }
+
+    ConstIterator const end() const { return m_rules.end(); }
+    Iterator end() { return m_rules.end(); }
+
+private:
+    NonnullRefPtrVector<CSSRule> m_rules;
+};
+
+}