LibWeb: Implement CountQueuingStrategy highWaterMark property

Userland/Libraries/LibWeb/Streams/CountQueuingStrategy.h

@@ -0,0 +1,43 @@
+/*
+ * Copyright (c) 2023, Shannon Booth <shannon.ml.booth@gmail.com>
+ *
+ * SPDX-License-Identifier: BSD-2-Clause
+ */
+
+#pragma once
+
+#include <AK/Forward.h>
+#include <LibJS/Forward.h>
+#include <LibWeb/Bindings/PlatformObject.h>
+#include <LibWeb/Forward.h>
+#include <LibWeb/Streams/QueuingStrategyInit.h>
+
+namespace Web::Streams {
+
+// https://streams.spec.whatwg.org/#countqueuingstrategy
+class CountQueuingStrategy final : public Bindings::PlatformObject {
+    WEB_PLATFORM_OBJECT(CountQueuingStrategy, Bindings::PlatformObject);
+
+public:
+    static WebIDL::ExceptionOr<JS::NonnullGCPtr<CountQueuingStrategy>> construct_impl(JS::Realm&, QueuingStrategyInit const&);
+
+    virtual ~CountQueuingStrategy() override;
+
+    // https://streams.spec.whatwg.org/#cqs-high-water-mark
+    double high_water_mark() const
+    {
+        // The highWaterMark getter steps are:
+        // 1. Return this.[[highWaterMark]].
+        return m_high_water_mark;
+    }
+
+private:
+    explicit CountQueuingStrategy(JS::Realm&, double high_water_mark);
+
+    virtual JS::ThrowCompletionOr<void> initialize(JS::Realm&) override;
+
+    // https://streams.spec.whatwg.org/#countqueuingstrategy-highwatermark
+    double m_high_water_mark { 0 };
+};
+
+}