LibWeb: Add CSSConditionRule

https://www.w3.org/TR/css-conditional-3/#the-cssconditionrule-interface

This simply exposes a condition string, which is implemented differently
in each sub-class.

Userland/Libraries/LibWeb/CMakeLists.txt

@@ -12,6 +12,7 @@ set(SOURCES
     Bindings/ScriptExecutionContext.cpp
     Bindings/WindowObject.cpp
     Bindings/Wrappable.cpp
+    CSS/CSSConditionRule.cpp
     CSS/CSSGroupingRule.cpp
     CSS/CSSImportRule.cpp
     CSS/CSSRule.cpp

Userland/Libraries/LibWeb/CSS/CSSConditionRule.cpp

@@ -0,0 +1,20 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#include <LibWeb/CSS/CSSConditionRule.h>
+
+namespace Web::CSS {
+
+CSSConditionRule::CSSConditionRule(NonnullRefPtrVector<CSSRule>&& rules)
+    : CSSGroupingRule(move(rules))
+{
+}
+
+CSSConditionRule::~CSSConditionRule()
+{
+}
+
+}

Userland/Libraries/LibWeb/CSS/CSSConditionRule.h

@@ -0,0 +1,29 @@
+/*
+ * Copyright (c) 2021, Sam Atkins <atkinssj@serenityos.org>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/NonnullRefPtr.h>
+#include <LibWeb/CSS/CSSGroupingRule.h>
+#include <LibWeb/Forward.h>
+
+namespace Web::CSS {
+
+class CSSConditionRule : public CSSGroupingRule {
+    AK_MAKE_NONCOPYABLE(CSSConditionRule);
+    AK_MAKE_NONMOVABLE(CSSConditionRule);
+
+public:
+    ~CSSConditionRule();
+
+    virtual String condition_text() const = 0;
+    virtual void set_condition_text(String) = 0;
+
+protected:
+    explicit CSSConditionRule(NonnullRefPtrVector<CSSRule>&&);
+};
+
+}

Userland/Libraries/LibWeb/CSS/CSSConditionRule.idl

@@ -0,0 +1,3 @@
+interface CSSConditionRule : CSSGroupingRule {
+    attribute CSSOMString conditionText;
+};